Spray a grill-friendly pan with non-stick cooking spray.
Add the mushrooms and onion.
1 8 oz package of sliced white mushrooms, ½ of a large sweet onion
Drizzle with the oil and sprinkle with salt.
2 teaspoon olive oil, 2 pinches of kosher salt
Place on a hot grill over medium to medium-low heat. Shut the grill and cook for 15-20 minutes tossing every 5 minutes.
I could have pulled them off sooner, but I wanted a few burnt and overcooked pieces-- I think it adds to the flavor. So I left them on the grill for an additional few minutes even placing them over a high flame to get a scorch.
Alongside I made London broil, broccoli and baked sweet potatoes, which I started in the microwave because I knew they would take the longest.
I sliced up the steak and piled on the mushrooms and onion.