Preparation Prepare grill for cooking over medium-hot charcoal (moderate heat for gas). While grill is heating, mince garlic, then mash to a paste with salt and pepper using a large heavy knife. Reserve half of garlic paste in a large salad bowl. Whisk together remaining garlic paste and 2 tablespoons olive oil in another large bowl, then add lamb and toss to coat. Divide lamb among skewers, leaving a little space between pieces (for even cooking). Whisk vinegar into reserved garlic paste, then add remaining 1/4 cup oil in a slow stream, whisking until emulsified. Add beans, celery, olives, pine nuts, and mint, then toss to coat. Grill lamb, turning as grill marks appear on each side, about 6 minutes total for medium-rare. Serve with bean salad.