Preheat oven to 350℉. Line 9x13-inch baking pan with parchment paper (or generously butter). Set aside.
In a large bowl, whisk together sweet rice flour, sugar, baking powder, spices, and salt.
Add in coconut milk, pumpkin puree, eggs, melted butter, and vanilla. Whisk until smooth. Scrape down sides and bottom of bowl to ensure through mixing. Batter should be smooth without any dry streaks of flour.
Transfer batter to prepared baking pan. Spread into an even layer. Forcefully bang bottom of pan against hard surface to remove any air bubbles.
TOPPING: Mix together sugar and cinnamon. Generously sprinkle mixture over mochi batter.
Bake for about 45-55 minutes until toothpick inserted in center of pan comes out clean. Mochi may rise and puff during baking. It will settle as it cools. Cool for an hour before slicing into desired portions. Best enjoyed the same day it is baked!