Combine all of the yogurt sauce ingredients in a glass bowl. Cover and refrigerate until needed. In another bowl combine all of the spices and olive oil. Coat the Beef Tenderloin Tips in the spices. Place on a skewer and marinate for 1 to 2 hours. Preheat grill to medium-high heat. While the grill is preheating combine the couscous, tomatoes, garlic, and red onions. Cover until needed.