Prepare the Romesco: Preheat oven to 375 degrees F. Line a baking pan with aluminum foil. Place garlic, almonds, bread, and tomato on baking sheet. Drizzle everything but almonds with olive oil. Roast in oven until almonds are toasted and bread is light golden brown, about 8-10 minutes. Remove almonds and bread from sheet pan and continue to roast cloves of garlic and tomato until soft, an additional 20 minutes. Remove from oven. When cool enough to handle peel skin from garlic and tomato. Add almonds, bread and garlic to bowl of food processor.
Meanwhile, Grill Peppers for Romesco Sauce: Heat grill to high, or turn flames to high on a gas stove. Char peppers over grill or flame until blackened and blistered all over. Transfer to a large bowl, cover with plastic wrap, and set aside to steam for 15-20 minutes. Remove from bowl and use paper towels or your fingers to remove the charred skin; discard. Remove and discard the stems, ribs and seeds.
Make the Romesco Sauce: Transfer peppers and remaining sauce ingredients, except olive oil, to the bowl of a food processor with almonds/bread. Pulse until combined. With the processor running, slowly add in the oil. Process sauce until smooth and well combined. Taste and adjust for seasoning. For a thinner romesco sauce, add olive oil, 1 tablespoon at a time, until desired consistency is achieved. Transfer sauce to a bowl, cover and set aside in the refrigerator until ready to use.
Prepare the Cauliflower Steaks: Trim the bottom stem from the cauliflower so it will stand upright on a cutting board. Cut vertically into 4 (¾ - 1’’ thick) slices (steaks).
Grill Cauliflower and Scallions: Preheat grill (or grill pan) to medium high and oil grates. Brush both the cauliflower and scallions with olive oil and season with salt. Grill scallions, turning frequently, until charred and soft, about 2-3 minutes. Grill cauliflower steaks until charred and cooked through, about 8 minutes per side. Remove from grill and sprinkle with grated parmesan.
Serve with romesco sauce.
Notes
*Romesco sauce will keep, covered in the refrigerator, for up to 5 days.