Slice your cauliflower lengthwise through the core. If it is medium-sized you should get 4 to 5 ‘steaks.’ If you’re using 2 small heads, you will most likely get 2-3 slices per head.
Place cauliflower and tomatoes on the parchment paper lined baking sheet. Drizzle with 2 tablespoons of olive oil and season to taste with salt, pepper, and onion powder.
Roast at 450 for 9 minutes. Broil an addition 1 to 2 minutes or until the edges the cauliflower steaks have browned and the tomatoes have blistered.
While the cauliflower is baking, combine the remaining tablespoon olive oil with the parsley and pumpkin seeds, and season with salt and pepper. When the cauliflower is done baking, spoon on a hearty amount of lemon tahini dressing and top with the herb mixture., and serve.