To prepare chicken skewers, cut chicken into 1-inch pieces and thread onto skewers; place in a shallow baking dish. Combine remaining ingredients for skewers in a bowl and mix well; pour over chicken. Cover and marinate in refrigerator for 8 to 24 hours.
When almost ready to serve, cook chicken skewers on a hot grill until lightly browned, about 10 minutes.
Meanwhile, prepare orzo: Cook orzo to al dente according to package instructions and drain. While pasta cooks, heat olive oil and butter in a large skillet over low heat. Add mushrooms and cook until slightly brown; drain.
Combine blue cheese, mascarpone, and mushrooms in a large bowl and mix well. Add spinach and pasta and toss until well blended. Season to taste and serve with warm chicken skewers.
Makes 12 servings.