Step 1) Gently shape ground beef into 5-inch burgers. Season burgers on both sides with 1 tablespoon seasoning.
Step 2) Grill over Direct Medium heat ( with the lid closed as much as possible), until the internal temperature reaches 160℉ for medium, 12 to 15 minutes, turning once.
Step 3) Heat oil in a large skillet; add mushrooms and 1 teaspoon seasoning. Cook until mushrooms are tender, about 5 minutes.
Step 4) Serve on hamburger buns, topping each burger with an equal amount of mushrooms.