Preheat oven to 350 F. Spray an 11x7 inch baking dish with cooking spray. Cook greens in broth and water in a medium pot over medium heat for 20 minutes or until desired tenderness; drain well and set aside. Melt butter in a medium saucepan over medium-high heat; add onion and garlic and cook for 4 minutes or until onion is translucent. Add chicken and ham; cook until heated through. Add rice and cook for 1 minute, stirring constantly. Stir in chicken stock, milk, salt and pepper and cook for 2 minutes. Combine cooked mustard greens with chicken and ham mixture. Pour into prepared baking dish. Sprinkle with cheese. Cover and bake for 45 minutes or until rice is tender.