In a large mixing bowl, combine ground beef, breadcrumbs, egg, and seasonings. For extra moisture, fold in grated onion or zucchini. Let sit while preheating the oven to 375°F.

Take small portions of the meat mix, flatten in your palm, place a cube of cheese in the center, and mold the meat around it to form balls. Arrange on a lined baking sheet.

Bake the meatballs for 25-30 minutes, or until browned and cooked through. Check with a meat thermometer to ensure it's at 160°F.

Cook the spaghetti according to package instructions. Drain, then toss with marinara sauce.

To serve, create a bed of saucy spaghetti on each plate, place meatballs on top, and garnish with fresh basil or grated cheese.