Cut tortillas into 1/2" strips. Dice onion. Fry both in plenty of oil on the griddle, stirring often until tortillas are crisp. Remove excess oil if necessary. Whisk eggs in a bowl and pour over tortillas and onion. Cook until firm. Pour enchilada sauce over eggs and heat until warm. Cover eggs with shredded cheese and tent with foil until the cheese melts. Heat and serve beans on the side (or drain them and mix in with the eggs halfway through cooking).