Preheat oven to 350 degrees to bake casserole
In a large skillet add ground beef and onion. Cook over medium high heat until ground beef is no longer pink and onion is softened. Stir in minced garlic, salt, pepper, chili powder, and ground cumin. Cook for 1 minute and turn off burner.
Spray a 2 1/2 quart baking dish with a non-stick cooking spray. Place 2 roasted poblano peppers flat into bottom of baking dish. Sprinkle 1 cup of shredded cheese over the peppers. Place 1/2 of the ground beef mixture over the cheese evenly.
Repeat layers with 2 roasted poblano peppers, 1 cup of cheese, rest of the ground beef mixture and top with 1 more cup of cheese.