ONE FREQUENT complaint from those who cook for two is that there are too many loose ends, or leftovers, because you can't buy things in small quantities.

Today's 30-minute meal makes an effort to put that complaint to rest for at least one of the ingredients by using it in two different recipes. Now that may sound repetitious, but the way the ingredient, in this case spinach, is used, it tastes completely different in each recipe.

For the main dish it is mixed with zucchini, which you can buy in any quantity you like, for a frittata. The spinach adds texture and body to the dish, but in the frittata it is hardly the primary flavor.

In the salad, on the other hand, the spinach is the predominant ingredient and uncooked it tastes and feels very different from the cooked version.

Between the 1/2 pound of spinach in the frittata and a cup, more or less, in the salad, all of the 10-ounce bag can be used at one meal.

Not everyone has access to loose spinach, and even when they do it doesn't necessarily look better or fresher than the packaged fresh spinach. This may be one of the few instances when loose produce is not necessarily better than packaged.

You will still have loose ends if you use these recipes, but the egg yolks can be frozen for use in hollandaise or cooked and used as garnish on a salad.

The cheeses will last long enough for you to think up other things to do with them. And the leftover onion can be used to season almost anything you cook the next night, or even three nights later.

Zucchini Frittata is an excellent choice for a summer menu when you don't want meant and you don't want to work too hard or get the kitchen too warm.

You can serve the pita bread on the side, but it really is delicious stuffed with some of the frittata. Stuffed or not, the pita is best warmed.

STAPLES: Garlic cloves, salad and olive oil, thyme, basil, rosemary, black pepper, 3 eggs, apple cider vinegar, Dijon mustard.

SHOPPING LIST: 1 1/4 pounds zucchini, 1 large shallot, 10-ounce package fresh spinach, small wedge parmesan cheese, 2 ounces monterey jack cheese, 2 large pita breads, 1 small red pepper, 1 small red onion (optional). MENU FOR 30-MINUTE MEAL ZUCCHINI FRITTATA* PITA BREAD SPINACH SALAD WITH GOLDEN DOOR DRESSING* BLUEBERRIES AND STRAWBERRIES *Recipes included ZUCCHINI FRITTATA (2 servings) 1 1/4 pounds zucchini 1 large clove garlic 1 large shallot 2 teaspoons salad oil 1/2 pound fresh spinach 2 tablespoons grated parmesan cheese 1 teaspoon dried thyme or 2 teaspoons fresh 1 teaspoon dried basil or 1 tablespoon fresh, mined 1 teaspoon dried rosemary or 2 teaspoons fresh Freshly ground black pepper to taste 3 eggs 2 egg whites 2 ounces monterey jack cheese

Wash and grate zucchini into a bowl. Mince garlic and shallot and saute in oil until soft. Wash spinach and shake dry. Drain off excess moisture from zucchini. Add with spinach and seasonings to pan and cook until softened and liquid is absorbed.

Grate parmesan. In separate bowl beat eggs and egg whites together. Add parmesan. Pour over zucchini mixture and cook until golden on the bottom. Grate jack cheese. Turn frittata with spatula. Sprinkle jack over frittata and allow to melt or run under the broiler, if desired.

Warm pita bread and serve frittata with bread. It tastes excellent stuffed into the bread. SPINACH SALAD WITH GOLDEN DOOR DRESSING (2 servings) 1 small clove garlic 2 tablespoons apple cider vinegar 2 tablespoons olive oil 1 teaspoon Dijon mustard 1/4 teaspoon black pepper 1 cup or more raw spinach 1 small red pepper or 1/2 or 1 large one 1 small slice red onion, optional

Put garlic through press. Combine with vinegar, oil, mustard and black pepper. Shake well or whip with wire whisk.

Cut pepper into julienne strips. Slice onion and separate into rings. Divide spinach between two serving plates. Place peppers and onion rings on top. Spoon on dressing.

(Each tablespoon dressing contains 60 calories.) GAME PLAN: Grate zucchini. Put garlic through press. Mince shallot. Wash spinach and shake dry. Saute garlic and shallot in hot oil. Grate parmesan and jack cheeses. Drain off moisture from zucchini. Mince basil if fresh is used. Combine zucchini, spinach and seasonings and add to pan. Beat eggs and whites, add parmesan. Slice red pepper. Slice red onion. Add eggs to zucchini and cook. Make salad dressing. Heat pita bread. Turn frittata and top with jack cheese. Arrange salad plates.