Preheat oven to 350 degrees. Wash vegetables. Chop onion, garlic and sweet potato. Slice green pepper and mushrooms. Wipe off top of can of tomatoes.
Heat oil in a large sauté pan and sauté the onion. Cook for about 5 minutes until onion is translucent. Then add the garlic and oregano.
Stir in tomatoes and bring to a boil. Add the green pepper, mushrooms and bay leaf. Let it cook for 5-10 minutes. Remove the bay leaf and then add cooked sweet potato and a pinch of salt.
Combine the queso and Monterey Jack cheese. Place a spoonful of tomato sauce mixture on the bottom of a large casserole dish. Put 3 to 4 tortillas on top of the sauce and sprinkle 1/3 of the cheese mixture on top of the tortillas.
Layer tortillas, cheese, sauce, ending with tortillas topped with cheese. Cover with foil and bake for 25 minutes.
Chop the cilantro and sprinkle it on top of the dish along with a dollop of yogurt.