Wash the potato and place it in the microwave and cook until tender, roughly 1 to 2 minutes, depending on your microwave. Let it sit until it's cool enough to handle. Then put it in a bowl and mash it with a fork. Measure out ½ cup of the mashed potato.
Place the lentils, garlic, dehydrated onions, bouillon, yeast flakes, oats, maple syrup, cornstarch, and spices in a food processor and pulse for several seconds. Use a spoon to push the ingredients down, add the mashed potato and flax egg, and pulse again until you have a thick mixture, leaving some texture from the lentils. Set aside.
Heat 1 tablespoon of oil in a skillet over medium heat, until it's shimmering.
Make 6 small patties from the bean mixture. Place patties on the heated skillet. Cook for 5 to 7 minutes until the patties are browned on the bottom and firm enough to flip. Turn the patties and add the rest of the oil. Cook the other side for an additional 5 to 7 minutes. Turn off the heat, cover, and keep the patties in the pan as it cools for another 10 minutes. They will firm up as they cool. Depending on the size of your skillet, you may need to cook these in batches.
Keep burgers in an airtight container in the fridge for up to 5 days. You can freeze them in a freezer-safe container or bag for up to 2 months.
Notes
If you don't have Better Than Bouillion, you can substitute an equal amount of miso paste.