Preheat oven to 375 degrees F (190 degrees C). Line 12 muffin cups with paper liners.
Soak chia seeds in the water in a bowl until thickened and paste-like, 5 to 10 minutes.
Whisk cashew flour, flax seed, coconut flour, tapioca starch, cinnamon, baking soda, and salt together in a bowl. Mix chia seed mixture, dates, walnuts, zucchini, applesauce, coconut oil, and stevia together in a separate bowl; stir into dry mixture until batter is just combined. Spoon batter into the muffin cups.
Bake in the preheated oven until a toothpick inserted in the middle of a muffin comes out clean, 30 to 35 minutes. Cool muffins in the muffin tin on a wire rack before removing, about 10 minutes; cool another 5 minutes before serving.
