Heat the oil in a large skillet, and saute the onion for about 4 minutes on medium heat. Add the yellow squash, zucchini, oregano, salt, cumin, garlic, and black pepper. Saute 5 minutes, stirring often.
Stir in the tomatoes and chile peppers. Transfer the mixture to an oven proof 2 1/2 quart casserole, cover, and bake for 30 minutes.
Stir in the cilantro, and serve immediately or let cool to room temperature. Enjoy!