Whisk 2 1/2 tbsp fresh lemon juice, 2 tbsp olive oil, 2 cloves crushed garlic and 1/2 tsp grated lemon peel in small bowl to blend. Stir in 2 tbsp fresh basil and 2 tsp drained capers. Season vinaigrette to taste with salt and pepper. (Can be prepared 1 hour ahead. Let stand at room temperature.) Prepare barbecue (medium-high heat) or preheat broiler. Season (4) 5- to 6-ounce halibut steaks with salt and pepper. Brush fish with 1 tbsp vinaigrette, dividing equally. Grill or broil halibut steaks until just cooked through, about 4 minutes per side. Transfer fish to plates. Rewhisk remaining vinaigrette; pour over fish. Garnish fish with basil and serve.