mix ground beef,spinach, onion & garlic 1 tsp salt & pepper in a large bowl.

warm oil in a large skillet over medium heat & gently shape neat mixture into 8 balls.

cook meatballs on all sides until cooked through, 12 to 15 minutes.

warm tomato sauce in a small saucepan over medium-low heat for 5 minutes.

spin 1 tbsp warmed sauce onto top & bottom of each roll, then sprinkle mozzarella on bottom halves.

top with a meatball. cover with top halves of rolls to make sandwiches.