Preheat the oven to 450°F.
Lightly grease a standard muffin tin with nonstick cooking spray.
In a large mixing bowl, crumble the lean ground beef.
Add the finely chopped onion to the ground beef.
Mix gently until the onion is evenly distributed.
Add the condensed vegetable soup, bread crumbs, egg, salt, and black pepper.
Mix until all ingredients are fully combined. Avoid overmixing, as this may cause the meatloaf muffins to become dense.
Portion approximately 3/4 c of the meat mixture into each prepared muffin cup.
Press the mixture gently into each cup without packing it too firmly.
Bake for 15 minutes, or until the meatloaf muffins are cooked through and reach an internal temperature of 160°F.
Remove the muffin tin from the oven and allow the meatloaf muffins to rest for a few minutes.
Carefully remove each muffin from the tin.
Serve warm with potatoes, vegetables, salad, macaroni and cheese, pasta salad, or crusty bread.