1. Bring 1 1/2 cups water to a boil in a large saucepan over medium-high heat. Add couscous, 1/4 teaspoon salt, and pepper to pan. Cover, remove from heat, and let stand 5 minutes. Fluff with a fork.
2. Heat a large skillet over medium-high heat. Add 1 tablespoon olive oil to pan; swirl to coat. Sprinkle shrimp with remaining 1/8 teaspoon salt. Add shrimp to pan, and sauté for 3 minutes or until done. Add shrimp to couscous mixture.
3. Combine remaining 2 tablespoons oil, tomatoes, onions, and olives in a large bowl; toss. Add tomato mixture to couscous mixture; toss to combine. Serve with yogurt.