Heat the oven to 375F
After rinsing the beans, spread them out on a sheetpan lined with paper towels and let them dry thoroughly while you prepare the rest.
Place oatmeal in food processor and process until they are ground into a coarse flour consistency (you can have some pieces of oats left, it will add some chewiness to the patties). Remove to a large bowl.
Process walnuts in food processor into small pieces. Do not overwork them or they will turn into a paste. They need to provide a slight crunch to the patties. Add them to the bowl.
Place mushrooms in food processor and pulse a few times until they are finely chopped.
In a large skillet, sauté onion in a tablespoon olive oil. Add garlic and mushrooms and a pinch of salt and cook until the moisture is mostly gone. Add the spices and stir until fragrant.
Transfer to the bowl. Add nutritional yeast (optional).
Place the beans in the food processor and pulse about 12 times (until they come together but are still a bit chunky). Add to the bowl.
Mix thoroughly with a fork.
Line sheetpan with parchment paper, spray with olive oil. Form 8 patties (about 1/3 cup each) with your hands and place them on the sheet. Spray more olive oil on top.
Bake 30 to 35 minutes, flipping carefully after 20 minutes so they bake evenly.
Serve immediately or freeze for future use, stacked between sheets of parchment paper in an airtight container or freezer bag.
Note: You can reheat them from frozen without thawing, on a medium-hot grill or in a pan 4 to 5 minutes on each side, or in the microwave for 60 to 90 seconds. If you freeze them before cooking, no need to thaw either, just add a few more minutes to the cooking time in the oven.