To make the burgers, heat a large sauté pan over medium heat and add the olive oil. Gently sauté the mushrooms and onions until lightly caramelized, 6 to 7 minutes.   

Stir in the garlic, cumin and coriander, and gently sauté until aromatic, about 1 minute. Set aside on a plate to cool.   

Place the beans in a large mixing bowl, and using a potato masher, mash the beans until mostly broken down and creamy. Stir in the mushroom-onion mixture, cooked quinoa, and season with salt and pepper to taste.   

Add the egg and breadcrumbs, and mix well.  

Form the mixture into 4 compact patties, and place on a plate. Set in the refrigerator to chill while preparing the avocado mayo.  

To prepare the avocado mayo, scoop the avocado meat from the skin and place in a bowl. Using a fork, mash the avocado until mostly smooth with some pieces remaining. Stir in the mayonnaise, and season with lemon juice, salt and pepper to taste. Set aside.   

Heat a cast-iron griddle or skillet over medium heat, and add the grapeseed oil.  

Cook the burgers on the first side until golden brown and crisp. Flip and repeat. Continue cooking until the burgers are hot all the way through. Note: If you’re using cheese, top the burgers with the cheese after you flip them over.  

Spread the bottom bun with the avocado mayo, and top with the burger. Top with the condiments and toppings of your choice, and serve.  

Note:  

To steam quinoa, place the quinoa and a pinch of salt in a saucepan. Pour in 2 times the amount of water to quinoa to the pot (e.g., 1 cup quinoa to 2 cups water), and bring to a boil. Reduce the heat to a simmer and cover. Cook, undisturbed, for 15 minutes. Remove from the heat and allow to steam an additional 5 minutes. Remove the lid, fluff with a fork and serve.