Heat the oven to 400°F. Lightly grease 8 cups of a standard muffin tin.
In a large bowl, combine the ground beef, egg, breadcrumbs, milk, diced onion, Worcestershire sauce, garlic powder, salt, and black pepper. Mix gently just until combined.
Divide the meat mixture into 8 portions. Press each portion into a greased muffin cup, making a small well in the center. Place one cheddar cube in each well, then cover it with the meat mixture and seal the top so the cheese is enclosed.
Brush the tops of the meatloaves with ketchup. Arrange the green beans in a single layer on a rimmed baking sheet and toss them with the olive oil.
Bake the muffin tin and green beans at the same time. Roast the meatloaves until cooked through, about 20 to 25 minutes, and roast the beans until tender with lightly browned edges, about 18 to 22 minutes. Check that the center of a meatloaf reaches 160°F.
Let the meatloaves rest in the tin for 5 minutes, then carefully lift them out. Serve with the roasted green beans.