Whisk brown rice flour, sorghum flour, millet flour, ground chia seeds, and baking powder together in a bowl. Whisk banana puree, walnuts, eggs, rice milk, applesauce, vegetable oil, salt, and cinnamon together in a separate large bowl. Whisk flour mixture into banana mixture until smooth, thick batter forms.
Heat a griddle or large skillet over medium-high heat. Drop batter by large spoonfuls onto the griddle, spreading as necessary to form pancake shape. Cook until bubbles form and the edges are dry, 3 to 4 minutes. Flip and cook until browned on the other side, 2 to 3 minutes. Repeat with remaining batter.