Marinate your patties with salt, pepper, and soy sauce. No need to wait longer than 30 minutes.
Slice your mushrooms. Heat up a skillet with a tbsp of olive oil. Add your mushrooms. Pinch of salt and pepper. Add half the soy sauce. Cook for 6 minutes, or until done. Remove.
Add another tbsp of olive oil. Heat up, Add your patties. Cook for 4 minutes on each side.
In a separate skillet, add a little bit of olive oil. Heat up, add the buns face down. Toast for a couple minutes and remove.
Slice a couple of slices of onion. Plate the burger. First bottom bun, then patty, mushrooms, onion, BBQ sauce, top bun.