Place the florets in pan with 1 1/2 cups water and heat to high until bubbling. Reduce the heat to medium and cover; steam for 5 minutes until the water cooks out and the cauliflower is slightly tender when pierced with a fork.
Place the steamed cauliflower on a baking sheet. Sprinkle it with garlic powder, kosher salt, and fresh ground pepper. Then use a brush to paint the BBQ sauce on both sides of each floret.
Place the cauliflower on the grill and cook until tender and blackened, about 4 minutes per side.
Remove the cauliflower from the grill and place it back on the tray. Use the same brush to brush each side of the florets with another coat of BBQ sauce. Serve immediately.