I recommend measuring the ingredients in grams on a kitchen scale.
Combine the wet ingredients in a mug and put aside.
Process the oats in an electric coffee grinder/blender or blender. Blend until they turn into flour (or just use store-bought oat flour).
Add all dry ingredients to a bowl.
Add wet ingredients into dry ingredients and stir with a spoon or whisk until just combined (don't overmix). The batter should form some bubbles because the baking soda will react with the lime/lemon juice.
Heat your waffle machine (I use low to medium heat). Once it's hot, lightly brush it with oil, spoon 2-3 tbsp batter (per waffle) in it, and cook for about 5 minutes (or as per the instructions of your waffle machine).
For two-colored waffles, split the batter into two parts. Add the remaining ingredients (cocoa or cacao powder, maple syrup, plant milk) to one-half of the batter and whisk. Spoon a little light batter into your heated waffle machine and then some chocolate batter.
Serve your waffles with maple syrup, a chocolate sauce or fruits, and enjoy!