Gently mix together the prepared meatballs with the spaghetti sauce in a small saucepan or microwave-safe dish. Heat the meatballs over low heat in a saucepan on the stove or in 1-minute intervals, covered, in a heat-safe dish in the microwave until just warmed through.
Mix together the olive oil with garlic and oregano and brush on the opened sides of the buns.
Place the buns onto a baking sheet and toast for 5 minutes, or until just browned.
Remove the buns from the oven and place 2 slices of provolone cheese on each bun, slightly overlapping to cover the surface of the bun. Top with 3 large (or 4 smaller) meatballs and an additional slice of cheese to cover the meatballs.
Return to the oven and bake for 5-7 minutes or until the cheese is melted.
Close the sandwich and serve meatball subs immediately.
Notes
Meatballs: Use any Italian-flavored meatballs you like for this recipe, keeping in mind that homemade meatballs are best. Spaghetti Sauce: Use your favorite, well-seasoned spaghetti sauce for the best flavor. Cheese: Thinly sliced provolone is best, but thicker sliced provolone or mozzarella can be used.