- With one rack in the middle position and a second rack in the lowest position, preheat the oven to 425°F (220°C). Line two baking sheets with silicone mats or parchment paper
- Remove the stems from the mushrooms. With a spoon, remove the black part underneath the cap of the mushroom (the lamellae or gills) and reserve them for a vegetable broth or compost them.
- Spread the vegetables out on the baking sheets. Toss with the oil. Season with salt and pepper. Roast for 30 minutes or until tender and golden. Remove the baking sheets from the oven and drizzle the lemon juice over the vegetables.
- Meanwhile, in a food processor, finely chop the beets and onion with the hoisin, steak spice and harissa. Add the chickpeas, oats and chickpea flour. Pulse for a few seconds at a time until the mixture forms a rough paste. Use a spatula to scrape down the sides of the food processor as needed. With your hands, form the mixture into 6 patties.
- In a large non-stick skillet over medium heat, brown half of the patties at a time in the oil until browned on both sides and firm.
- In the same skillet, toast the inside of the burger buns. Spread generously with mayonnaise. Layer with the patties, roasted vegetables, beets and lettuce.