Preheat the oven to 350 degrees and line a baking sheet with parchment paper.
In a large bowl, combine the ground beef, crushed Ritz crackers, egg, milk, Parmesan cheese, Italian seasoning, minced garlic, chopped onion, salt, and black pepper.
Mix the ingredients with your hands until they are evenly distributed but not overworked.
Shape the mixture into a loaf about 8 inches long and place it on the prepared baking sheet.
Spread the marinara sauce evenly over the top of the loaf.
Bake for 55 to 60 minutes until the internal temperature reaches 160 degrees.
Remove the meatloaf from the oven and let it rest for 10 minutes before slicing.