Preheat the grill to 400-500 degrees F. Prepare the aluminum foil by tearing off two 12x18" pieces.
In a large mixing bowl, combine the cauliflower florets, white beans, quartered onion, and garlic cloves. In a measuring cup, mix together the olive oil, garlic powder, rosemary, salt and pepper. Pour this over the veggies and beans and mix until everything is coated.
Transfer equal amounts of the veggie/bean mixture to each piece of foil. Make the foil packets by folding the aluminum foil in half over the mixture, then folding in each side.
Place each packet directly on the grill, close, and cook for 15-20 minutes, or until the cauliflower is tender. To check if it's ready, use a fork to carefully pierce one of the packets and test a floret of cauliflower.
Carefully remove from the grill and tear off the top of each packet. Serve the packets by themselves as a light meal, or on the side of grilled fish or burgers.