Creating the Chile Rellenos Casserole is straightforward when you follow these step-by-step instructions:

1. Preheat: Preheat your oven to 350°F (175°C) and grease a 9×13-inch baking dish.

2. Prepare Chiles: Roast the poblano or Anaheim chiles over an open flame or under the broiler until the skin is charred. Place them in a bag or covered bowl for a few minutes to steam, then peel and seed them.

3. Layer Chiles: Once peeled, slice the chiles open to lay them flat. Arrange half of the chiles in a single layer in the greased baking dish.

4. Add Cheese: Sprinkle half of the Monterey Jack and cheddar cheese evenly over the chiles.

5. Repeat Layer: Place the remaining chiles on top of the cheese layer, followed by the rest of the cheese.

6. Mix Egg Mixture: In a separate bowl, whisk together the eggs, half-and-half, garlic powder, onion powder, cumin, salt, and pepper until well combined.

7. Pour Mixture: Carefully pour the egg mixture over the layered chiles and cheese in the baking dish.

8. Top with Tomatoes: Evenly spread the diced tomatoes on top of the casserole.

9. Bake: Bake in the preheated oven for 30-35 minutes, or until the casserole is set and golden brown on top.

10. Cool: Remove from the oven and let it cool for about 5-10 minutes before serving to allow the flavors to meld.