Preheat oven to 375º F and lightly grease a 9×5-inch loaf pan.
Heat olive oil in a large pan or skillet over medium-high heat and sautè onion and bell pepper for 10 minutes, or until softened.
Add garlic and cook for 1-2 minutes, or until fragrant. Season generously with salt and pepper.
Remove from heat and set aside.
Combine meat, egg, breadcrumbs, Worcestershire sauce and red pepper flakes together in a large bowl, and mix together until combined. Season generously with salt and pepper, then mix in pepper and onion and cubed provolone until incorporated.
Place mixture in loaf pan and bake for 45-50 minutes, or until cooked through.
Melt butter in a medium saucepan over medium heat, then whisk in flour to create a roux. Cook for 2-3 minutes, or until golden brown.
While whisking continuously, slowly pour in milk until incorporated and smooth, then cook for 4-5 minutes, or until thickened.
Remove sauce from heat and mix in grated provolone and parmesan cheese until melted.
Remove meatloaf from oven and pour cheese sauce over the top.