Preheat oven to 350℉ and prepare a baking sheet by lining it with parchment paper. Set aside
In a large bowl, add ground beef, diced onions, bell peppers, 1 cup of cheddar cheese, eggs, garlic, ketchup, Worcestershire sauce, bread crumbs, ⅓ cup of milk, salt, black pepper, and paprika. Mix until just combined.
Shape the meat into a loaf and position it in the center of the prepared baking sheet. Bake in the oven for 50 minutes.
10 minutes before the meatloaf is done baking. Melt butter in a skillet over medium heat. Saute onions until soft and translucent.
In a sauce pan over medium-low heat, add milk and cream chees and whisk continuosly until the cream cheese is blended into the milk.
Add cornstarch, salt, garlic powder, mustard powder, and onion powder. Whisk until well incorporated.
Slowly add cheddar cheese into the sauce whisking continuously until completely melted and incorporporated.
Remove the meatloaf from the oven and let it rest for 5 minutes. Then, pour the cheese whiz sauce over the top and top with sautéed onions before serving.