In a skillet, cook beef over medium heat until no longer pink; drain. Add the green pepper, salt, pepper, oregano and garlic powder. Cook until green pepper is tender. Combine cheddar and Monterey Jack cheeses; set aside.
In a 2-1/2-qt. baking dish, layer half each of meat mixture, chiles and cheese; repeat with remaining meat mixture, chiles and cheese. Meanwhile, in a bowl, combine the egg, cream and flour; pour over cheese layer.
Bake at 350° for 35 minutes. Remove from oven; cover with tomato sauce. Sprinkle with additional cheese if desired. Bake 10-15 minutes longer or until set.