If you haven't cooked the lentils, start there. Otherwise, start by giving the mushrooms a large chop. Saute them over medium head with the onion and a large dash of salt for about 7 minutes, touching as little as possible.
Stir in the tomato paste and miso. It won't completely break down, just get everything coated.
Add the mushrooms, green onion, and lentils to a blender or food processor and give it a few pulses. You want to break it down a bit, but be careful not to puree it. You want it a little chunky.
Add this mixture to a bowl with a little more salt and pepper. Stir in the flour, garlic powder, and egg. Stir through the breadcrumbs last.
Form into 4 patties. If you have time to refirdgerate, even for 15 minutes, do it. If not start cooking. Cook in a greased pan over medium heat for about 4 minutes per side. Until browned and slightly crispy.