In a suitable sized saucepan, bring 1 cup of water to a boil, add the couscous and cover tightly with a lid. Remove from heat and let sit for about 5 minutes.
In a large, deep bowl, combine chopped tomatoes, parsley, mint, lemon juice, olive oil and ¼ teaspoon salt. Mix the soaked couscous with the resulting vegetable mixture.
In a separate bowl, combine unsweetened yogurt, mint, lemon juice and crushed garlic. Season with ½ teaspoon pepper and ¼ teaspoon salt and mix thoroughly.
Grease the preheated grill with vegetable or any other oil. Place the lamb steaks on the greased grill grate and fry on each side for about 2-3 minutes.