Preheat oven to 180 degrees C (356 F) and line a oven tray.
Place the Portobello mushrooms, whole, on the lined tray and drizzle with a little olive oil and a pinch of sea salt. Pop in the oven to roast for around 12 minutes.
Remove from the oven to cool.
Add the drained black beans to a large bowl and mash them with a fork to break some of the beans up. This should only take about 10 to 15 seconds. Don't go overboard.
Next, place a 1/2 cup of the rolled oats in to a food processor and pulse for around 10 seconds or until the oats resemble a rough meal.
Roughly chop the cooked mushrooms and add them to the processor with the red onion and pulse again two or three times.
Add the remaining whole oats, the nutritional yeast, the rosemary, garlic powder, salt, pepper, chilli flakes, BBQ sauce, soy sauce, tapioca, cooked lentils and mashed black beans to the processor. Pulse together until the mixture comes together - you may need to stop occasionally to scrape down the sides and stir the mixture a little. When ready the mixture will be wet but firm enough to bring together in to a pattie. See the picture above for reference.
Remove the blade from the processor and line a large tray with greaseproof paper. Take a portion of the burger mixture, enough to fit in to the white of your palm, and shape it in to a patty. Place the finished patty on the lined tray and continue with the remaining mixture. I rinse my hands every so often - the mixture is a little wet and rinsing your hands just makes the process easier.
The patties are fine to go on the pan now or you can cover them and pop them in the fridge to further firm up.
To cook the burgers, heat a glug (around 1 tablespoon) of olive oil on a skillet or frypan over medium heat. When hot add 3 or 4 of the burgers to the pan depending on your pan size. Cook the burgers on one side for 3-4 minutes or until the bottom is seared well before flipping it over to cook on the other side. Press the burgers gently with a spatula to flatten a little. Turn down the heat to low-medium and cook the other side for another 3-4 minutes. Repeat with the remaining burgers.
Serve on a burger bun with your favourite condiments. I love mustard, fresh lettuce, BBQ sauce and onion.
The burgers will keep for 3 to 4 days in the fridge in a sealed container or freeze for up to 2 months. If you are stacking the burgers to store, place a sheet of grease-proof paper between each layer so the burgers don't stick together.
Add the ingredients to the processor in the order listed to ensure a well texture burger.