Pizza, an adopted-from-Naples American favorite, has never been considered a healthy diet food. Yet, as Grunes points out, pizzas contain four food groups and, by using certain low-fat and low-sodium ingredients, can be made virtually fat-free. Each of her more than 100 combinations features nutritional data. For those who shudder at fashioning crusts from scratch, substitutes include bagels and pita, lahvosh and flatbread, among others. Some of the mixtures (e.g., mango salsa, and bok choy and tofu) are decidedly upscale; others will appeal to hearty palates--for instance, southwest chili, fajita, and turkey and onion pizzas. Food inventions galore for cooks willing to spend some time in the kitchen or over a grill.