01 -
Preheat the oven to 375 degrees and spray a large loaf pan with cooking spray.
02 -
In a large skillet, add the butter and the onions and bell peppers, mushrooms, salt and pepper. Let brown for 1-2 minutes before stirring, then let brown for another 1-2 minutes before stirring again. Let cool for five minutes.
03 -
In a large bowl add the ground beef, ketchup, Worcestershire sauce, eggs, panko breadcrumbs and the cooled vegetable mixture.
04 -
Add half the mixture to your loaf pan then add half of the cheese to the middle of the pan in a 2 inch wide section (I cut the slices into thirds for the right width). Cover with the rest of the meat and form into a rounded top loaf shape.
05 -
Cook for 40 minutes, then pull out of the oven, cover with remaining cheese and put back in. Cook for 15-20 minutes, then let rest for 10 minutes before cutting.