Place chicken in a resealable plastic bag set in a bowl. In a small bowl stir together yogurt, lemon juice, mustard, cinnamon, curry powder, salt, and crushed red pepper. Pour over chicken. Seal bag; turn to coat. Refrigerate for 1 to 4 hours, turning occasionally.
Preheat broiler. On 6 long metal skewers, thread chicken, sweet pepper, and squash, leaving 1/4 inch between pieces. Broil 4 to 5 inches from heat for 8 to 10 minutes or until chicken is no longer pink, turning once. If desired, serve with pita bread and Tomato Relish. Makes 6 servings.
Combine Roma tomatoes, grape tomatoes, balsamic vinegar, oregano, thyme, honey, and garlic. Add salt and ground black pepper to taste. Cover; chill up to 4 hours.