Preheat the oven to 350 degrees and lightly grease a loaf pan.
In a large bowl, combine the ground beef, breadcrumbs, egg, milk, Italian seasoning, garlic powder, onion, salt, and black pepper.
Mix the ingredients with your hands until evenly combined but do not overwork the meat.
Transfer the mixture to the prepared loaf pan and press it into an even shape.
Spread the marinara sauce evenly over the top of the meatloaf.
Bake for 50 to 55 minutes until the internal temperature reaches 160 degrees.
Remove from the oven and let the meatloaf rest for 5 minutes before slicing.