In large skillet, heat olive oil and saute the onions and bell peppers over medium heat until tranparent and golden brown, then add the chopped green chiles. Add the prepared squashes and cook until soft. Stir in corn (and tomatoes, if desired) and simmer until the liquid has cooked down. Salt and pepper to taste and add a dash of oregano.
If you want to add drained whole pinto beans or chopped spinach, do so here and simmer until heated through and then add the remaining ingredients, the cheddar and Cojita cheeses, sour cream and minced cilantro.