Heat the olive oil in a skillet over medium heat. Add the onion and cook until softened, about 5 minutes. Add in the mushrooms and cook until browned, about 5 minutes. Add in cumin, chili powder, cayenne pepper and a generous pinch of salt/pepper and stir together. Set aside.
Place the black beans in a large bowl and roughly mash, keeping some of the beans whole.
Add in the cooked quinoa and cooked mushrooms and stir together to combine. Stir in the finely chopped walnuts and mix to form a batter. It should stick together when pressed between your fingers.
Lightly spray a baking sheet and form mini-burger patties. Place on the baking sheet and cook for 35-40 minutes until crispy and browned.
Add the sliders to the buns and top as desired. I love these both with a dollop of guacamole, slice of cheese, chopped peppers and a slice of tomato.
Notes
*The walnuts act as a binder, you want them finely crumbled but not a paste. I pulse them in a food processor until crumbs form.