Preheat oven to 400°. Line muffin pan with cupcake liners.
In large bowl, thoroughly mix cake mix with pumpkin. Divide evenly into liners. Liners will be full.
Mix flour, brown sugar, sugar, and cinnamon together. Cut cold butter into flour mixture using either a pastry blender, a fork, or 2 knives. Mixture will become crumbly.
Spoon the streusel evenly onto muffin batter. Bake for 20 min. or until toothpick comes out clean. Enjoy!
Here's a trick I use with these muffins. Spoon a little streusel onto the raw muffin batter, and tamp it down with the back of your spoon. This makes room for more streusel, and the batter won't stick to the spoon.