Sauté the Aromatics: Heat the olive oil in a large frying pan over a medium heat. Add the finely chopped red onion and cook for 5-7 minutes, until softened and translucent. Add the minced garlic and cook for another minute until fragrant.

Cook the Mushrooms: Add the finely chopped mushrooms to the pan. Cook for 8-10 minutes, stirring occasionally, until they have released their liquid and it has evaporated. The mushrooms should be well-browned. This step is crucial for developing a deep, savoury flavour.

Combine the Base: Transfer the cooked mushroom and onion mixture to a food processor. Add the rinsed and drained black beans, toasted walnuts, soy sauce, smoked paprika, and ground cumin.

Pulse, Don't Blend: Pulse the mixture 8-10 times, until roughly combined but still with plenty of texture. You don't want a smooth puree. I find that this is the secret to a burger with a great bite.

Form the Patties: Scrape the mixture into a large mixing bowl. Add the rolled oats, panko breadcrumbs, and the lightly beaten egg. Season generously with salt and pepper. Mix everything together with your hands until just combined.

Shape and Chill: Divide the mixture into four equal portions and shape them into patties about 2cm thick. Place them on a plate or baking tray lined with greaseproof paper and chill in the fridge for at least 15 minutes (or up to a few hours). This helps them firm up.

Cook the Burgers: Wipe out the frying pan you used earlier and add a little more olive oil. Heat over a medium-high heat. Carefully place the chilled patties in the pan and cook for 5-6 minutes per side, until a dark, handsome crust has formed and they are heated through. If using cheese, place a slice on top of each patty during the last minute of cooking and cover the pan with a lid to help it get gloriously melty.

Assemble and Serve: Lightly toast your burger buns. Assemble your burgers with the cooked patties and your favourite toppings. Serve immediately.