Place hoagie rolls, open faced on baking sheet. Drizzle olive oil lightly over surface of rolls. Place in a preheated 400 degree oven for 5 minutes until rolls are slightly toasted.
Spread marinara sauce on each side of bun. Add meatballs and drizzle a bit more marinara sauce on top of meatballs. Sprinkle with Parmesan cheese.
Return to oven for 10 minutes. Test to ensure meatballs are heated through.
Serve with extra marinara sauce for dipping (optional)