Preheat the oven to 375°F (190°C). Grease a 9x13-inch baking dish lightly with olive oil or non-stick spray.

Heat a large skillet over medium-high heat. Add ground beef and cook, breaking it apart with a wooden spoon until browned and no longer pink, about 10 minutes. Drain excess fat and set beef aside.

In the same skillet, add olive oil. Toss in sliced bell peppers, onions, and minced garlic. Cook until softened and fragrant, about 5-8 minutes. Season lightly with salt and pepper.

Return the browned beef to the skillet with veggies. Stir to combine and let flavors meld over low heat for 2 minutes. Remove from heat.

Spread half of the beef-veggie mixture evenly in the baking dish. Top with half of the provolone slices, then half the cheddar cheese. Repeat layers with the remaining beef mixture and cheeses.

Place the casserole in the preheated oven and bake for 20-25 minutes until cheese is melted, bubbly, and slightly golden on top.

Let the casserole cool for 10 minutes before slicing into 5 equal portions to help it set for clean slices.