1. In a medium skillet, saute onion and garlic in 2 tablespoons of olive oil until softened.
2. Add beans, saute 2 minutes. Stir in lemon juice and arugula; heat through. Season with salt and pepper to taste; set aside.
3. Brush swordfish with 2 tablespoons olive oil; sprinkle with salt and pepper.
4. Grill on high 3 to 4 minutes per side, turning once.
5. To serve place cooked bean mixture on a serving plate. Lay fish on top and sprinkle with balsamic vinegar.