Grilled tuna steak with vegetable vinaigrette recipe

Ingredients

• 4 170g (6oz) center-cut tuna steaks (about 2cm/¾ inch thick)
• 4 tbsp extra-virgin olive oil, for drizzling
• 1 pinch sea salt and freshly ground black pepper
• 1 lemon, cut into wedges
• 1 small red onion
• 1 small head radicchio
• 120 ml extra-virgin olive oil
• 3 tbsp sherry vinegar
• 1 tsp sea salt
• 1 small clove of garlic, minced
• 2 tbsp capers
• 2 crumbled dried piquín chillis or generous pinch red pepper flakes
• 1 small handful fresh mint or parsley leaves, coarsely chopped
• 1 small handful fresh marjoram or oregano leaves, coarsely chopped
• 1 fennel bulb, trimmed