Peel and mash the sweet potato until smooth. Sift the flour, cumin, salt and baking powder into a mixing bowl.
Whisk together the gram flour and almond milk. Gradually whisk the wet ingredients into the dry until you have a smooth batter.
Grease a waffle iron liberally with coconut oil, sprinkle in a little of the nigella seeds and heat until hot. Cook the batter in batches until all the batter is used up, keeping the waffles warm as you go.
Peel and slice the avocado, top the waffles with sliced avocado and rocket, then serve with a couple of lime wedges on the side to squeeze over.