Preheat oven to 350 degrees F. Grease mini cupcake pan(s) with butter.
Combine rice flour, quinoa flour, pumpkin spice, ginger, baking powder, baking soda, and salt in a mixing bowl. Mix thoroughly.
Beat eggs, sugar, canola oil, and pumpkin until smooth and fluffy.
Pour flour mixture into pumpkin mixture slowly and mix at a low speed until thoroughly combined and batter is smooth.
Pour batter into greased mini muffin pans. Fill to just beneath the rim.
Bake for 20-25 minutes at 350 degrees F on the middle rack. Poke a toothpick through the center of one of the cupcakes. It should come out clean. If not, bake for a few more minutes.
Meanwhile, combine cream cheese and butter with a mixer until really smooth. Add the sugar, 1/2 cup at a time, mixing after each addition. Add vanilla and mix until smooth.
Let the cupcakes cool for 10 minutes before frosting.
Frost generously using a butter knife or icing spatula. Sprinkle walnuts on top (optional).