Preheat a grill to medium high and lightly oil the grates. Mix the tandoori marinade and 1 tablespoon yogurt in a small bowl. Season the lamb chops with salt and pepper. Rub all over with the yogurt mixture. Let sit at room temperature, 10 minutes.
Meanwhile, mix the remaining 1/4 cup yogurt with 1 tablespoon water, the cilantro, grated garlic, lemon juice, 2 pinches of salt and a grind of pepper in a small bowl.
Toss the green beans, tomatoes, vegetable oil, sliced garlic, cumin seeds, 1 teaspoon salt and a few grinds of pepper in a large bowl. Spread out the vegetables on a large sheet of heavy-duty foil. Bring the short ends of the foil together and fold to seal; fold in the sides to form a packet.
Place the packet on the grill and cook until the vegetables are lightly charred and the tomatoes start to burst, about 10 minutes. Grill the lamb chops 2 to 3 minutes per side for medium doneness. Divide the lamb and vegetables among plates. Top with cilantro and serve with the yogurt sauce.