Make the sunflower romesco: In the bowl of a food processor, combine the sunflower seeds, roasted red peppers, garlic, paprika, cayenne, vinegar, tomato paste, parsley, salt, and pepper. Pulse the mixture until all ingredients are finely chopped and lightly pasty. Scrape the bowl down. With the motor on low, drizzle the olive oil through the feed tube until sauce is creamy. Check for seasoning and set aside.
Rinse the food processor. Make the herbed tahini cream. In the food processor combine the lemon juice, garlic, maple syrup, salt, parsley, green onions, and rosemary. Pulse the mixture until herbs are finely chopped. Add the tahini and pulse to combine. It will get pasty. With the motor running, drizzle in the ice water until you have a smooth, fluid, slightly aerated sauce. Check for seasoning and set aside.
Preheat the oven to 400°F.
Make the whole roasted cauliflower: using a paring knife, cut into the core of the cauliflower on an angle to expose the “branches” and crevices of the cauliflower. Flip the cauliflower right side up and place in a steamer basket. In a large pot, bring a couple inches of water to a boil. Once boiling, carefully drop the steamer basket in and close a lid on tight. Steam the cauliflower for 10 minutes. The exterior should yield to a poke from a paring knife.
Carefully extract the cauliflower from the pot and dry off the surface thoroughly. Flip the cauliflower over and spoon some of the romesco into the crevices. Shake and tap the cauliflower to work it in.
Line an oven-proof skillet or baking sheet with parchment paper and place the cauliflower inside, right side up. Brush the exterior with olive oil and season with salt & pepper. Transfer to the oven and set a timer for 10 minutes.
After 10 minutes, take the cauliflower out and brush it liberally with romesco. Place the cauliflower back in the oven for another 35-40 minutes, or until browned, dry on the exterior & yielding when poked with a knife.
Serve whole roasted cauliflower hot on a platter with more romesco, herbed tahini cream, and garnishes of choice.