Preheat your grill to high heat (450-500 degrees). Place a cast iron skillet over the heat for the tomatoes.
After removing the leaves from the cauliflower, trim off just the end of the stem. Cut each head of cauliflower directly down the middle. Cut one steak from the center of each half and reserve the rest of the cauliflower florets for later use.
Drizzle the steaks with olive oil and season with salt and pepper. Set the steaks on the grill and cook for 3-4 minutes per side.
While the cauliflower grills, add the olive oil to the cast iron skillet followed by the tomatoes. Once the tomatoes start to burst, add the green onions, garlic, salt and pepper to the pan. Cook for 2 additional minutes and remove from the heat.
Serve the grilled cauliflower steaks with the warm tomato salad spooned over the top. Top with the balsamic glaze and fresh basil, if desired.