1. In food processor, mix together red peppers, almonds, oil, vinegar, garlic, paprika, and 1/4 tsp each salt and pepper until combined; set aside. Pat flank steak dry with paper towel; season with remaining salt and pepper.
2. Preheat grill to medium-high; grease grates well. Grill steak turning once, for 10 to 12 minutes or until medium-rare. Let steak rest for 10 minutes. Slice thinly against the grain.
3. Layer kale, olives, steak slices, 2 tbsp Romesco sauce and cheese in each bun. Return to grill over medium heat; cook for 2 to 3 minutes or until bun is toasted and cheese is melted.
• Refrigerate leftover Romesco sauce for up to a week in an airtight container. Serve on burgers, sausages or grilled cheese sandwiches.
• Substitute fresh mozzarella or Fontina for Gruyère cheese if desired.