1. Preheat oven to 400 degree. Chop cauliflower into bite sized pieces. Toss with olive oil, salt, and pepper. Spread out onto lined baking sheet and roast for 30-40 minutes.
2. While cauliflower is roasting, make romesco sauce. Combine all sauce ingredients, except for olive oil, in a food processor. While running, stream in olive oil. Mix until combined.
3. Remove cauliflower from oven and set aside for now.
4. To assemble tacos, warm tortillas and spread romesco sauce on the bottom. Top with cauliflower, chopped cilantro, green onions, crushed toasted peanuts, and a squeeze of fresh lime.