Preheat oven to 450°F. Fill a large pot half-way and season with 3 tablespoon kosher salt. Bring to a boil.
Meanwhile, trim the stem of your cauliflower so it has a sturdy base and can rest floret-side up without support. When the water is boiling, place the cauliflower floret-side down in the pot and cook for 10 minutes, or until you can easily slide a fork into the florets. Remove and let steam on a wire rack until it cools to room temperature, about 20 minutes.
While you wait, make the sauce. To a blender add 2 roasted red peppers, 1 teaspoon paprika, ½ teaspoon cayenne, 2 tablespoon sherry vinegar, 1 peeled garlic clove, and ¼ cup olive oil. Blend until smooth. Set aside.
Mix 3 tablespoon olive oil with ½ teaspoon turmeric and remaining ¼ teaspoon paprika. Using a pastry brush, generously cover the cooled cauliflower. Sprinkle with ½ teaspoon salt. Place on a sheet pan and roast for 30 minutes, or until golden and slightly charred on the edges.
While the cauliflower roasts, prepare your garnish. Roughly chop the hazelnuts and place them in a small bowl. Season with 2 tablespoon olive oil, zest of 1 lemon and a generous pinch of flaky salt. Mix and set aside. Next, roughly chop enough parsley to fill ½ cup and add it to a second small bowl. Top with the juice of half the lemon and a pinch of kosher salt. Toss and set aside.
When the cauliflower is golden brown and charred on the edges, remove from the oven. Lay it on a base of pepper sauce and seasoned hazelnuts. Finish with chopped parsley and the remaining lemon juice.