Ingredients: one medium onion, 1-2 cloves of garlic, a few summer squash (or a lot), 2-3 sweet peppers, and anything else that looks good. 

Directions:  Finely chop the garlic, then cut all other veggies into long thin strips (roughly 1/4 inch thick).  Heat 1-2 tablespoons of oil in a heavy skillet, throw the garlic and veggies in, and cook over medium-high heat, stirring frequently.  When veggies have started to soften, stir in 2-3 teaspoons of your favorite chili powder (more or less, to taste), or a mixture of 1/2 teaspoon each of ground cumin, ground coriander, red chili flakes, salt, and black pepper.  Stir till veggies are evenly coated in spices, taste and adjust seasonings, and continue to cook till veggies and reach your desired level of firmness for eating.  Spoon everything into warmed tortillas and add any or all of the optional additions:  cheese, beans, salsa, and sour cream.  For meat-eaters, you can startby sautéing strips of chicken, beef, lamb, etc., before the veggies, and stir all together before serving.