1. Preheat your oven to 375°F (190°C) and lightly grease a 9×13-inch baking dish.
2. In a large skillet over medium heat, add olive oil and sauté onions until translucent, about 3-4 minutes.
3. Add garlic and cook for another minute before adding the ground beef. Cook until browned, breaking it apart with a spatula, about 5-7 minutes.
4. Stir in the cumin, chili powder, salt, and pepper to taste. Remove from heat and set aside.
5. In the prepared baking dish, layer the roasted poblano peppers, followed by half of the beef mixture, and then half of the cheese.
6. Repeat the layers with the remaining beef and cheese.
7. In a mixing bowl, whisk together the eggs, milk, flour, and baking powder until smooth. Pour this mixture evenly over the casserole.
8. Bake in the preheated oven for 30-35 minutes or until the top is golden and set.
9. Let it cool for a few minutes before slicing and serving. Enjoy with a side of salsa if desired!

Remember, patience is key here. Letting the casserole rest before serving helps the flavors meld beautifully, just like my abuela used to do with her dishes.