1Heat oven to 350°F. Spray 2 1/2-quart shallow casserole with cooking spray. Cook frozen cauliflower as directed on bag. Cook frozen rice as directed on package. Set aside.
2In 4-quart saucepan, melt 3 tablespoons of the butter. Cook onion in butter about 4 minutes, stirring occasionally, until softened. Stir in flour and mustard with whisk; cook about 1 minute. Slowly stir in milk. Cook and stir until bubbly and slightly thickened. Stir in cooked cauliflower, ham and chile slices. Spoon into casserole.
3In small microwavable bowl, microwave remaining 3 tablespoons butter uncovered on High about 1 minute or until melted; stir in bread crumbs. Sprinkle over vegetable mixture in casserole.
4Bake 25 to 30 minutes or until bubbly around edge. Let stand 5 minutes before serving.