In a medium sized bowl add the sausage, milk, breadcrumbs, garlic, egg, and onion mix everything to combine.
Line a sheet pan with parchment paper place the broccoli on the sheet pan. Roll the meatball mixture into uniform-sized balls about 1 1/2 inch diameter.
Bake for 18 minutes then flip the meatballs and pour 3 tbs of marinara sauce on each meatball then sprinkle with the mozzarella cheese bake for an additional 5 minutes. Enjoy!