In a large bowl, combine mashed bananas, oil, eggs and sugar. Mix until combined. Add in flour, baking soda, cinnamon, salt, walnuts and coffee. Mix until just combined. Scoop batter into greased or lined muffin pans.
In a small bowl, combine brown sugar and 1 tsp cinnamon. Sprinkle this mixture over the tops of the muffins.
Bake at 350F for about 18-20 minutes for jumbo muffins, 12-15 minutes for regular muffins or until toothpick inserted comes out clean. Remove from pan and let cool about 10 minutes on a wire rack.