Combine the soymilk, pumpkin, brown sugar, oil, ground flaxseed, lemon juice, and vanilla extract in a medium bowl and mix thoroughly. Allow to sit for 5 minutes.
While the liquid mixture is sitting, combine the buckwheat flour, tapioca flour, rice flour, baking powder, baking soda, cinnamon, salt, ginger, nutmeg, and clove in a large bowl and stir with a whisk.
Pour the liquid mixture into the flour mixture and stir until well blended, and until any large clumps of rice flour are gone.
Let the waffle batter stand for 3 to 5 minutes while preheating a waffle maker according to the manufacturer's directions. This will allow the rice flour to absorb more of the moisture.
Stir the batter more if necessary to get rid of any remaining rice flour clumps.
Spray both grids of the waffle iron generously with oil. This is especially important with vegan and gluten-free waffles, to avoid sticking--even if you have a "non-stick" iron. Pour or ladle the batter onto the center of the iron, covering no more than two-thirds of the iron's surface for the first waffle. Adjust the amount as needed for subsequent waffles.
Bake each waffle for 3 to 5 minutes, or until it can be removed easily, spraying both grids generously with oil prior to each waffle.