Preheat your oven to 350°F (175°C).
Brown the sausage, ground beef, and onion. Drain any fat.
Prepare the baking dish: Grease a 9×13-inch casserole dish. Layer half of the meat mixture at the bottom.
Layer half of the green chiles over the meat mixture. Each layer will take about one and a half cans of chiles.
Layer the cheese. Sprinkle 1.5 cups of the shredded cheese over the peppers.
Repeat the layers. Add the remaining meat mixture, the rest of the peppers and top with the rest of the cheese.
Mix the egg batter: In a bowl, beat the eggs, milk, flour, salt, and pepper until smooth. You may add tabasco sauce or taco seasoning to the batter. Pour this mixture evenly over the meat, peppers and cheese.
Bake: Place the casserole in the oven and bake for 45-55 minutes, or until the egg mixture is set and the top is golden.
Garnish and serve: Let it cool for a few minutes, then sprinkle with cilantro and green onions if desired before serving.