Rinse the sweet potatoes.
Steam them for 20 minutes or until a knife passes easily through the center.
Remove from the heat and rinse in cold water. Peel.
Put the sweet potato in a potato ricer and mince it in a large bowl.
Cube the onion finely and add it to the sweet potato.
Season with all the spices and add the flax meal. Stir and set aside to bind.
Take a handful of the mixture and roll it into the sesame seeds. Rinse and slice the other vegetables and assemble the burger. Enjoy with a homemade mayo or mustard on the side.