1. Heat 1 tablespoon of the oil in a skillet over medium-high heat. Add mushrooms and cook until browned and moisture has released (3-5 minutes).
2. Move mushrooms to a bowl and chill until cooled (15-20 minutes).
3. Dissolve both bases in warm water. Pour over cooled mushrooms.
4. Season ground beef with pepper and Worcestershire sauce. Mix in the mushrooms until thoroughly combined. Form into four patties of desired thickness.
5. Heat the skillet over high heat. Add the remaining tablespoon of oil, then the burgers. Cover with a lid and let cook until seared (2-3 minutes). Flip, leave lid off, and cook to desired doneness (2-5 minutes).
6. Place burgers on buns and top with vegetables.