To a bowl, add 2 tbsp of ground flax seeds plus 6 tbsp of water. Give it a stir and set it aside.
Rinse the canned lentils, add them to a bowl, and using a fork or an immersion blender mash them. Then get a big mixing bowl and start combining all of the ingredients. First, add the mashed lentils, then the flax egg, and gluten-free flour.
Next, soak bread slices, squeeze out all the water from the bread and add it to the mixing bowl. Then chop scallions and parsley and add them to the bowl as well.
Lastly, make the mustard sauce. In a small bowl, combine yellow mustard maple syrup (or agave). Add only 1/2 of the mustard sauce to the burger mix and (reserve the other half for serving).
Using your hands mix everything together until incorporated.When the burger mixture is ready you can start forming the patties. If you don’t want to cook them right away you can refrigerate the patties for up to 2-3 days or freeze them for up to 3 months. Heat up a little bit of olive oil over medium heat in a skillet for at least five minutes. Once the skillet is thoroughly heated, cook the burgers on each side for about 3-5 minutes.
Assemble the burgers to your liking, here I used salad, tomatoes, pickles and a generous amount of the muster sauce.