Many years ago Al Capp, the cartoonist who invented Li'l Abner, also invented something called a Shmoo. The Shmoo was mankind's ultimate pet. A small, eternally cheerful beast, the Shmoo gave service with a smile; he provide both milk and meat: you kicked a Shmoo and he was grateful for the attention. Not the least of their qualities was fecundity; they proliferated like rabbits gone berserk. And finally, like most do-gooders, they managed to make a bloody nuisance of themselves.

One can't be sure where Al Capp got his inspiration for the Shmoo. However, did you ever notice how much they resembled zucchinis?

Zucchinis are the elongated dark green summer squash that appear mysteriously in gardens everywhere. Not only do they appear, they grow - mushrooming overnight from blossom to grotesquerie. Leave your garden for a day and you will find that zucchinis have taken over whole sections, leaning against your string beans, sprawling over your strawberries, crushing your corn. Pick one zucchini and two new one will appear.

Of course you cook as many as you can. And then you start giving them away to friends, to neighbors, to strangers, to anyone. There is one sensible solution to the zucchini explosion. It is called ratatouille - pronounced "rat-a-too-ee" - and it is a vegetable stew that is good either hot or cold.

The Staples: Olive oil, garlic, salt, pepper, eggs, butter, dry white wine, brown sugar.

The Shopping List: 4 medium onions; 1 small eggplant; 4 zucchinis; 3 green peppers; 5 large ripe tomatoes;1/2 pound bacon; 1 bunch parsley; 1/4 pound parmesan cheese; 1 pound spaghetti; 6 large ripe peaches.

5 P.M.: Take 2 of the onions, peel them and chop them into small pieces. If your eyes start to tear, try peeling the onions under cool running water.

Now the 3 green peppers. Cut away the seeds and slice the peppers into narrow strips. (If your eyes start to tear at this point, you're just unhappy.) Put a splash of olive oil into a large pan over medium heat and add the chopped onions and the peppers. Now add 2 cloves of garlic, minced fine. Cook for 6 or 7 minutes, until the onions seem tender.

Slice the zucchinis crosswise, making the slices about 1/4 of an inch in thickness. Peel the eggplant, cut it into bite-sized cubes and add both the zucchini and the eggplant to the pan.

While these vegetables are all stewing together, you peel the tomatoes. No, not that way. The easiest way to peel a tomato is to dip it briefly into boiling water and then rinse it under cold water. The skin will slide away easily. Some purists would suggest that you remove the tomato seeds, but I've never been able to figure out how that's done. Cut the tomatoes into small chunks and add them to the pan, along with some salt, pepper and a small fistful of minced parsley.

The ratatouille can be kept simmering over a very low heat until dinner time. Or it can be stored in the refrigerator and served cold.

5:45 P.M.: Start the spaghetti water boiling in your largest pot - 4 to 6 quarts of water for a pound of spaghetti.

Peel an onion and chop it fine, then saute it in a little oil in a saucepan over medium heat. In 4 or 5 minutes add the bacon, cut into small pieces. Cook for 5 or 6 minutes more, then add 1/2 cup of dry white wine.

In a second bowl, beat 2 eggs and then add the grated parmesan cheese, salt and a generous amount of freshly gound pepper.

6:20 P.M.: Add the spaghetti to the briskly boiling water and cook it for the minimum recommended time on the box, until it is cooked but chewy.

6:30 P.M.: Make sure that the ratatouille is hot (if it's supposed to be hot) or cold (if that's your plan).

As the spaghetti finishes cooking, drain it and transfer it to a large bowl. Immediately add the egg-and-cheese mixture and toss it together. Next add the bacon-and-onion mixture and toss it all together one more time.

The only trick to a meal like this is one of timing, of getting the various dishes cooked and served on some kind of schedule. Should either the spaghetti or the ratatouille not be completed on schedule, there's one easy solution - simply serve the dinner as two separate courses.

Five or 10 minutes before the end of the meal, steal out to the kitchen and peel the peaches the same way that you peeled the tomatoes. Cut them into halves. Take out the pits. Spoon brown sugar over each half and add a dab of butter. Put them under the broiler for just a few minutes, just until the butter is melted and the peaches are heated through. You can serve the peaches (canned peach halves can be used) with cream, with whipped cream, with brandy, with flaming brandy, or just by themselves, leaving well enough alone.