Cut tomatoes in half, then score the inside membrane with a knife several times. Drizzle tomatoes with olive oil. Sprinkle with steak seasoning and parmesan.
Preheat lightly greased grill to 350°F (medium setting).
Place tomatoes on a sheet of heavy-duty aluminum foil. Place foil with tomatoes on grill and grill over indirect heat, with grill lid closed, for 25 to 45 minutes. Check halfway through grilling, so the Parmesan cheese does not burn.