Prepare the meatballs according to package directions (oven or stovetop). Once heated through, gently simmer them in the tomato sauce for 5–7 minutes so they absorb flavor.
Lightly brush the inside of each bun with olive oil and toast in a skillet or oven until warm and just crisp at the edges.
Place 3 saucy meatballs into each bun. Spoon extra tomato sauce over the top.
Generously sprinkle with Parmesan cheese and garnish with fresh basil leaves.
Serve immediately while the meatballs are hot and the bread is soft with a slight crunch.