In a large bowl, mix together the yogurt, lemon juice, half the garlic, 1 teaspoon salt and the cumin. Transfer half the yogurt mixture to a small bowl. Add the shrimp to the large bowl and mix; cover and refrigerate for 15 minutes.
In a medium saucepan, heat 1 1/2 tablespoons olive oil, the crushed red pepper and remaining garlic over medium heat for 2 minutes. Add the chickpeas and cook, stirring, for 4 minutes. Add the tomatoes and remaining 1 teaspoon salt, cover and cook for 5 minutes. Lower the heat and keep warm until ready to serve.
Rub a grill pan with the remaining 1/2 tablespoon olive oil and heat over high heat. Add the marinated shrimp and grill, turning once, until cooked through, about 3 minutes on each side.
Top the chickpeas with the shrimp and serve with the reserved yogurt sauce.