Cut the ends off the onions, peel and slice into 1cm thick rings. Separate the layers to create your rings. I prefer to keep 2 layers together for a thicker onion ring.
In one bowl, combine all the wet mix ingredients and whisk well. In another bowl, combine the dry mix ingredients.
Dip each ring into the wet mix, followed by the dry mix. Transfer into the air fryer basket (or alternatively, a baking tray if cooking in the oven), ensuring not to overlap them. Lightly spray with oil and air fry each batch for 10 min or until golden and crispy.
In the meantime, add vegan mince and onions into a bowl and mix well (volume-wise they should be in a 1:1 ratio). Divide into 4 even sized balls.
Heat griddle or cast-iron skillet over medium-high heat. Add a splash of oil (any with a high smoke point) then add in the balls. Press down and flatten with a spatula. Try to get the patties as thin as possible. Cook on one side for 1-2 mins until browned, flip, season with salt and pepper, top with cheese and cook with lid on for 2 mins until cheese has melted. In the meantime, toast buns separately until edges start to brown.
To assemble, spread the sauce to the bottom of both buns. Top with 2 patties each, followed by the tomatoes, pickles, lettuce and other half of the buns.
Serve with onion rings and enjoy immediately!