Start by preheating a skillet over medium heat. Add the raw walnuts and toast them for about 5-7 minutes, stirring occasionally until they are golden and fragrant. Once done, remove them from the heat and let them cool before chopping them into smaller pieces.

In a food processor, pulse the finely diced mushrooms and white onion until both are finely chopped but not pureed. This should take just a few seconds.

Heat a tablespoon of oil in the same skillet over medium heat. Add the mushroom and onion mixture, seasoning it with a pinch of salt and pepper. Cook for about 6-8 minutes, stirring occasionally, until the moisture evaporates and the vegetables become tender.

In the food processor, combine the oats, Panko breadcrumbs, toasted walnuts, nutritional yeast, ground flax, and parsley. Pulse the mixture briefly to blend everything together, ensuring a nice mix for your veggie burger foundation.

Next, add drained black beans, BBQ sauce, and tamari into the food processor with the dry ingredients. Pulse until combined, leaving some chunks of beans for texture.

Transfer the cooked mushroom and onion mixture into a large bowl. Add the blended dry mixture and fold everything together until well combined.

Using a packed 1/2-cup measure, form the mixture into 8 large patties. Place them on a parchment-lined baking sheet.

Preheat your oven to 350°F (175°C). Bake the patties for 15 minutes, then carefully flip them over. Bake for an additional 12-15 minutes until the patties are firm and slightly golden brown.