Add to hot skillet, remaining 1/2 cup grated onion, fresh garlic and tomato paste.
Stir, heat for about 1 minute until combined.
Stir in crushed tomatoes, season with salt and pepper.
Place meatballs in bottom of shallow baking dish.
Pour heated sauce over meatballs making one even level of food in the dish.
Brush both sides of sliced baguette bread with a little olive oil.
Place baking dish at one end of sheet pan. Place sliced bread on baking sheet.
Bake for 7 minutes. Flip bread and bake 8 minutes more.
Remove from oven.
Place bread on top of meatballs in baking dish.
Top the bread with the provolone cheese, overlapping cheese, if necessary.
Set broiler to HIGH and cook until cheese melts. Watch closely should only take 2-3 minutes.
Using knife or spatula, separate casserole into two halves; making sure 2 slices of bread are in each portion.
Divide between two plates. Drizzle over any additional sauce left in the baking dish. Serve.