Cut the crusts off of the bread slices. Blend in a food processor until a breadcrumb consistency. This can also be done by hand but will result in larger pieces and will take longer.
In a medium bowl combine the ground beef, green bell pepper, onion, breadcrumbs, milk, garlic powder, and salt. Mix to combine.
Shape the beef mixture into the meatballs, approximately 1.5 inches in diameter. See notes about size and cooking times. Line the meatballs on a silicone baking sheet or parchment/foil and bake until completely cooked through, approximately 15 minutes.
While the meatballs are cooking, make the cheese sauce. Melt the butter in a small saucepan over medium low heat. When melted, add the flour and whisk to combine. Cook, whisking occasionally, until the roux is a light brown color, approximately 1-2 minutes.
Add the milk and whisk to combine. Turn the heat up to medium heat.
When the milk is warm, add the provolone cheese, salt, and pepper of choice. Whisk occasionally over medium heat until the cheese is melted and the sauce is thickened, approximately 5 minutes.
Serve the meatballs and cheese sauce warm.
Notes
This mixture makes approxiomately 32 meatballs when 1.5 inches in diameter before being cooked. Meatballs 1.25 inches in diameter (very small size) will make approximately 40 meatballs.If you use a ground beef that has a higher fat content, the meatballs will shrink more.It is recommended to cook ground meats all the way through for safety.