Heat oven to 350°F. Spray 8-inch square (2-quart) baking dish with cooking spray. In medium bowl, mix first 7 ingredients. Press in bottom and up sides of baking dish to within 1/2 inch of top.
In 2-quart saucepan, heat water, milk, butter and 1/4 teaspoon salt to boiling. Remove from heat; stir in potatoes. Let stand 30 seconds. Stir in egg. Stir in broccoli and cheese. Spoon over meat shell.
Bake 25 to 30 minutes or until meat loaf is thoroughly cooked and meat thermometer inserted in center of meat reads 170°F. Let stand 5 minutes; drain liquid along edges.