1. Preheat oven to 375°F (190°C). Line a baking sheet with parchment paper or lightly grease a loaf pan.

2. Heat olive oil in a skillet over medium heat. Add onions, green peppers, red peppers, and garlic. Sauté for 5–6 minutes until softened. Remove from heat and let cool slightly.

3. In a large bowl, combine ground beef, breadcrumbs, eggs, milk, Worcestershire sauce, salt, and pepper. Mix gently until just combined.

4. Stir in the cooled vegetable mixture until evenly distributed.

5. On the prepared baking sheet or in the loaf pan, shape half the meat mixture into a loaf shape.

6. Lay 4 slices of provolone cheese over the center of the loaf, leaving edges free.

7. Place the remaining meat mixture on top and shape to seal the cheese inside.

8. Bake for 45–50 minutes, or until the internal temperature reaches 160°F (71°C).

9. Remove from the oven, place the remaining 4 slices of provolone on top, and return to the oven for 2–3 minutes until melted.

10. Let rest for 5–10 minutes before slicing and serving.