Nobel prize winner Linus Pauling surely caused a stir when he said vitamin C could cure the common cold. Though many swear by the advice, researchers find the hypothesis difficult to prove.

But when Pauling said vitamin C could be used to treat and prevent cancer, eyebrows (and tempers) really began to rise.

Still, says Dr. Walter Mertz, director of the Human Nutrition Research Center at Beltsville, "he is partially right."

It turns out that the vitamin C in certain vegetables may have a protective effect against cancer-causing substances. Many vegetables, such as spinach, contain a great deal of nitrate, a compound that, combined with other compounds in the body, may be carcinogenic. Yet many of the same vegetables that contain nitrates also contain vitamin C, and it appears that the vitamin C prevents the conversion of nitrates into cancer-causing compounds.

"That's the beauty of good nutrition," says Mertz. "Nature provided a protective factor . . . there's nothing that's all-good or all-bad."

Variety is the key, he says, and if the color is still in the vegetables, so are the vitamins. Thus, it's best to cook vegetables as little as possible, retaining the color--and the vitamins.

Good nutrition isn't difficult, even when you have time for only a quick trip through the express lane of the supermarket. The following dinner should take no more than that, provided you have flour, sugar, salt, pepper and butter and/or oil on the shelf at home.

EXPRESS LANE LIST: chicken, dijon-style mustard, bread or bread crumbs, spinach, yogurt, cheese, onion, winter squash. BETTY'S MUSTARD CHICKEN (4 servings) 2 1/2- or 3-pound broiler-fryer chicken, cut into serving pieces 3 tablespoons melted butter 2 to 3 tablespoons dijon-style mustard 1 1/2 cups bread crumbs (make bread crumbs in a blender if desired) Ground pepper

Melt butter and stir in mustard. Coat chicken pieces with mixture. Combine crumbs and pepper. Dip chicken into bread crumbs and place in shallow baking pan. Do not overlap. Bake at 350 degrees for 40 minutes. BAKED WINTER SQUASH

Halve an acorn or hubbard squash, seed it, sprinkle with a little salt, if desired. Cover each half with aluminum foil. Bake at 350 degrees for 45 minutes or until tender.

Alternately, you can serve frozen, mashed winter squash cooked according to package directions. SPINACH CASSEROLE (4 servings) Excellent made with fresh spinach. 10 ounces fresh spinach (or 10 ounces frozen, chopped spinach) 2 tablespoons butter or oil 1 small onion, chopped 2 tablespoons flour 1/2 teaspoon each salt and freshly ground pepper 1/2 cup plain yogurt 1/2 cup grated cheddar or parmesan cheese

Wash the spinach and chop it. Place in a heavy skillet with a lid and steam until wilted (no need to add water or vegetable oil), stirring occasionally. Remove to a small bowl. (If using frozen spinach, place over low or medium heat to thaw and allow excess water to evaporate, then remove to a bowl.)

Melt butter in skillet. Add onion and cook until transparent. Add flour and stir 1 minute over medium heat. Season with salt and pepper and gradually whisk in the yogurt. Add spinach and turn to coat. Remove from heat, blend in cheese, pour into a greased 8-inch loaf pan and bake 20 minutes at 350 degrees.