1. Pierce sweet potatoes and Yukon Gold potatoes; microwave, uncovered, on high for 4 minutes, turning once.
2. When potatoes are cool enough to handle, peel and cut into 1/2-in. slices. Sprinkle with 4 teaspoons Cajun seasoning, 1/8 teaspoon salt and 1/8 teaspoon pepper.
3. Place potato slices on a grilling grid; transfer to grill rack. Grill, covered, over medium heat for 15-20 minutes or until tender, turning occasionally.
4. In a large bowl, combine the yogurt, lemon juice, garlic and remaining Cajun seasoning, salt and pepper. Gently fold in the arugula, tomatoes, olives, onions and potatoes. Yield: 8 servings.