In large bowl, combine muffin mix (reserve cinnamon packet) and water; mix well. Add blueberries and stir until combined. Pour batter into greased 9 x 13 pan. In bowl, combine melted butter, reserved cinnamon packet and walnuts. Sprinkle crumb topping over batter. Bake 400° for 30 minutes. Cool 10 minutes. Serve warm. Makes 12 servings.