Special equipment: 8 metal or wooden skewers if using wooden skewers, soak them in water in a casserole dish or baking sheet for 30 minutes prior to grilling. Prepare a grill or grill pan for medium-high heat; oil the grill grates with olive oil. Mix 3 tbsp balsamic vinegar, 3 tbsp lemon juice and 1 tbsp Dijon mustard in a small bowl. Add 2/3 c. olive oil in a slow stream while whisking. Season with salt and pepper. Thread 2 pounds swordfish, cut into 1-inch pieces, 1 medium head fennel, cut into 1-inch pieces and 1 pint grape or cherry tomatoes onto 8 skewers, alternating between fish and vegetables. Season with salt and pepper and brush the balsamic mixture over all the skewers. Add the skewers to the grill and cook until there are clear grill marks on the flame side, 3 to 5 minutes. Flip the skewers and cook for an additional 3 to 5 minutes. Continue to rotate the skewers and cook on each side until all sides are cooked and have a slight char. Serve hot!