Trim the fat off the lamb and cut the meat into 1-inch cubes.
In a medium bowl, whisk together ½ cup of the chopped mint, the crushed garlic, ½ cup of the yogurt, the wine, 1⁄8 teaspoon of the salt, and 1⁄8 teaspoon of the pepper.
Add the lamb cubes and toss to coat evenly.
Cover the bowl with plastic wrap and set in the refrigerator to marinate for exactly 1 hour.
If you are using wooden skewers, soak them in water for at least 10 minutes.
Slice each shallot into 4 large chunks. Cut the bell pepper in half, discard the seeds, and cut into 2-inch pieces.
Preheat a grill or a grill pan over medium-high heat.
Remove the lamb from the marinade, allowing the excess to drip off. (Discard the marinade.)
Thread each skewer with 2 to 3 pieces of the lamb, 2 pieces of shallot, 2 tomatoes, and 2 pieces of bell pepper.
Grill the kebobs, turning them several times, until the lamb is browned and cooked through, 12 minutes.
Meanwhile, make the mint-yogurt sauce: Mince the remaining clove of garlic.
In a small bowl, whisk together the remaining ¼ cup chopped mint, the minced garlic, the remaining ½ cup yogurt, and the remaining 1⁄8 teaspoon salt and pepper until thoroughly combined.
Set 2 lamb skewers on each of four plates and place 2 tablespoons of the mint-yogurt sauce on the side.