Divide the Worcestershire evenly on the insides of the mushroom caps. Sprinkle with the steak seasoning. Allow to marinate while you preheat a grill pan or outdoor grill.

Prep the buns by dividing them in half, then spritzing or brushing them with a bit of olive oil and sprinkling them with salt and pepper.

Grill the portobellos until soft and well marked, about 7 minutes per side. Before serving, add a slice or two of cheese and allow to melt. In the last 3 minutes of grilling, toast the insides of the buns until lightly golden.

Serve the burgers on the toasted buns with your choice of toppings. Enjoy!