Begin by making the quick pickled onions ahead of time. In a large jar, combine the onion slices, orange juice, lemon juice, lime juice, vinegar and salt. Securely tighten the lid of the jar and shake it vigorously. Chill the onions in the fridge for at least 2 hours, or preferably overnight. Store the pickled onions in an airtight container in the fridge for up to 4 weeks.

To make the veggie burgers, preheat the oven to 400°F (204°C). Line a large baking sheet with parchment paper.

While the oven is preheating, heat a large cast-iron skillet over medium heat and add about 1 tablespoon (15 ml) of water. Add the onion and garlic and sauté them for 2 to 3 minutes, until the onion is slightly tender and fragrant. Add the mushrooms and carrot and sauté the mixture for 3 to 4 minutes, until the veggies are crisp-tender. You may need to add a little more water to deglaze the skillet as the veggies are cooking. Remove the skillet from the heat and let the veggies cool for about 5 minutes.

Transfer the veggie mixture to a food processor. Add the chickpeas, oats, oat flour, flaxseed, tomato paste, cumin, coriander, paprika, chili powder,salt, black pepper and coconut aminos. Pulse the ingredients eight to ten times, until they are well combined but not pureed. Scrape down the sides of the food processor between pulses if needed. The mixture should be a doughy texture with some chunkiness retained from the vegetables and chickpeas. If the mixture is a little too wet to the touch, add additional oat flour 1 tablespoon (6 g) at a time.

Divide the mixture into eight even portions. Create the patties by rolling each section into a ball and flattening it between your palms. Place each patty on the prepared baking sheet, spaced 1½ inches (4 cm) apart.

Bake the burgers for 30 minutes, flipping them halfway through the baking time.

While the burgers are baking, prepare the classic burger sauce. In a medium jar, combine the yogurt, Sriracha and mustard. Use a fork to whisk the ingredients together. Taste the sauce and adjust the spiciness with extra Sriracha or the tang with extra mustard.

To prepare the must-have burger toppings, place the burger buns on a large baking sheet and warm them in the oven for the final 2 minutes of the burgers’ baking time. Alternatively, you may place the buns directly on the oven rack to warm them. Assemble your burgers by layering the buns with the lettuce, tomatoes, avocado, quick pickled onions, a burger patty, the classic burger sauce and microgreens. Serve the burgers with the cornichons on the side.

Any leftover burgers can be frozen, stored in a reusable bag or container, for up to 6 months. To reheat the burgers, thaw them and reheat them in a skillet over low heat for 2 to 3 minutes perside. Alternatively, you can grill the leftover burgers over low heat on lightly oiled grates or a lightly oiled piece of aluminum foil for 2 to 3 minutes per side.