Heat a large sauté pan over medium high heat and drizzle with 2 tablespoons of olive oil. Add the mushrooms, sweet potato, garlic, scallions and salt. Sauté for 5 – 7 minutes or until the mushrooms begin to brown and the sweet potato is just cooked through. Add the spinach, cumin, and cayenne and continue sautéing the vegetables until the spinach is wilted, about 2 – 3 minutes. Remove pan from the heat.

In a large bowl, add the black beans and mash with a potato masher until about ½ of the beans are smashed and the remaining beans are still whole. Add the sautéed vegetables to the beans and stir to combine. Form into 4 burgers and place on a platter.

Heat the same sauté pan to medium high heat and add the remaining 2 teaspoons of olive oil. Cook the burgers for 3 – 4 minutes per side or until crispy and browned. Remove to a platter. In a small bowl combine the yogurt, chipotle powder, and smoked paprika for the Spicy Yogurt Sauce.

Serve burgers on whole wheat buns with sliced tomatoes, lettuce, and a dollop of the Spicy Yogurt Sauce.