Wash the cauliflower and trim off all the leaves and the bottom of the stem. Place it stem-down on your cutting board. Cut it in half straight down through the middle. Take each half and make another parallel cut so that you have two “steaks,” about 1/2 to 3/4-inch thick. Make one more parallel cut on each half, to try to get a total of 4 steaks. Don’t worry if your final cut results in your cauliflower falling to pieces! How many steaks you get depends on the size and shape of your cauliflower. Reserve the individual florets for another use, or toss them with some hummus and roast them, too. (Individual florets will take less time, so be careful not to burn them.)
Sprinkle one side of each cauliflower steak with salt and pepper and place it pepper-side down on a non-stick or silicone-coated baking sheet. Spread hummus lightly on the top of each cauliflower piece and sprinkle with fresh rosemary, if you want. Bake until cauliflower is just tender and hummus is beginning to lightly brown, about 30 minutes.