Heat the oven to 375°F. Lightly grease a 12-cup muffin tin.
In a large bowl, gently mix the ground beef, egg, breadcrumbs, 2 tablespoons of the salsa, chili powder, cumin, garlic powder, and salt. Stop mixing as soon as the ingredients are combined so the meatloaves stay tender.
Divide the beef mixture among 8 muffin cups. Press it in lightly, leaving the tops rounded. Spoon the remaining salsa over each portion.
Bake for 18 to 22 minutes, until the meatloaves are cooked through. Sprinkle the cheddar over the tops during the last 3 minutes of baking, then let the muffins rest for 5 minutes before removing them from the tin.
While the meatloaves bake, combine the black beans, corn, red bell pepper, cilantro, lime juice, and olive oil in a bowl. Stir gently and taste, adding a little more lime juice if desired.
Serve the meatloaf muffins with the black bean corn salad alongside.