Make the BBQ sauce, if you don’t already have some on hand, to allow the flavors to infuse while you prepare the mushrooms.

Thinly slice the mushrooms. They should look shredded. Heat the oil in a large skillet on medium heat. Depending on the size of the pan, you may need to cook the mushrooms and onions in two batches. When the oil is hot, add the mushrooms and onions and stir frequently until the mushrooms lose their water and the onions become translucent and soft, approximately 5 to 7 minutes.

Turn up the heat to medium-high and add salt and pepper to taste. Cook until the onions caramelize and the edges of the mushrooms begin to crisp up, approximately 5 minutes.

When the mushrooms and onions are done cooking, add the BBQ sauce to the pan and stir until the mushrooms are completely coated in the sauce. Bring the mixture to a boil on medium heat and then reduce the heat to a low simmer. Cook for 15 minutes, stirring frequently, until the sauce is thick and sticky.

Serve the mushrooms on the buns and top with the arugula, tomato and sliced pickles.