Preheat the oven to 350°F.
Make the meatballs: Add all meatball ingredients to a large mixing bowl and mix until well combined. Form into 16 equal meatballs.
Arrange on a baking sheet and bake for 20 minutes.
Make the cheese sauce: Melt the butter in a small saucepan. Stir in the flour until completely combined. Whisk in the milk until completely smooth. Bring to a gentle boil, then turn the heat to low. Stir in the cheese until melted.
Place the meatballs in an even layer in a large sauté pan. Evenly drizzle with the marinara sauce. Place on medium heat and simmer, covered, for 10 minutes.
Slice open the buns and spread some garlic butter on the inside of each bun. Broil in the oven for a couple minutes, until lightly toasted.
Add 4 meatballs to each bun and top with extra marinara sauce and some of the cheese sauce.