Remove meat from lobster and cut into 1/2-inch pieces (leave claws whole, out of shell, if using Maine lobster). Place in a large mixing bowl. Add celery, onion, tomatoes, garlic, basil, mint, olive oil, lemon juice and toss. Season with salt and pepper and let stand 10 minutes. Add arugula, toss to coat and serve sprinkled with lemon zest.