For the steak:
Rub each steak on both sides with some of the olive oil and seasonings. Grill over high heat, turning just once, to desired doneness.
For the onions:
Put some of the chopped garlic, 2 tablespoons butter, and a teaspoon of seasoning on the cut side of each of 4 onion halves. Top each with the another half. Wrap each onion completely in aluminum foil, and bury in the hot coals for about 10 minutes, until quite soft. Move to the grates to finish cooking, another 5 minutes or so. The onions should be golden and soft to the point of falling apart.