In a 12” skillet, preferably cast iron, heat the olive oil over medium-high heat. Add mushrooms, red onion and garlic. Sauté while stirring occasionally until browned and tender, about 5 – 7 minutes. Set aside to cool slightly. (Use the same skillet to cook the burgers later).

Meanwhile, in a large mixing bowl mash the black beans with a potato masher to a lumpy texture. Most of the beans should be broken and some of them creamed. Add the sautéed mushroom-onion mixture, parsley, breadcrumbs, flaxseed, oregano, cumin, coriander, chili powder, salt, pepper and egg. Mix all the ingredients together really well.

Cover the bowl with plastic wrap and chill in refrigerator for 2 hours. Working with a chilled mixture makes it easier to form the burgers. Form the chilled mixture into 4 equal sized burgers, pressing them firmly, and place on a parchment paper lined baking sheet. Refrigerate to keep them cold, or freeze until needed.

Cook the burgers cold from the refrigerator. If the burgers are frozen, thaw them in refrigerator for at least 2 hours or longer before cooking (and in this case you may have to add a few minutes to the cooking time).

Heat a 12” cast iron skillet over medium-high heat until really hot. Add 2 teaspoons oil and then the burgers. Cook without disturbing for 4 – 5 minutes, reducing the heat as necessary. Gently flip the burgers over, adding another 2 teaspoons of oil if necessary, and cook for another 4 – 5 minutes. The burgers should be crisp and golden-brown on the outside and heated through on the inside.

Transfer the burgers onto hamburger buns and garnish with desired toppings. Suggestions: hamburger buns, cheese slices, leaf lettuce, micro-greens, tomatoes, onions, avocado, mayonnaise and sriracha sauce mixture, or other burger garnishes as desired.