Preheat the Blackstone griddle to medium-high heat. Add the green pepper, onion, and mushrooms. Toss with olive oil and cook until crispy. Transfer the veggies to the low heat side of the griddle.
In a small pot, combine all the cowboy butter ingredients. Mix well and place the pot on the low heat side of the griddle to warm and reduce.
Toss the sirloin cubes in olive oil and Montreal steak seasoning.
Move the cooked veggies to the low heat side of the griddle. Add the seasoned sirloin cubes to the hot side of the griddle and sear until cooked to your liking.
Stir the cowboy butter sauce and adjust seasoning if needed.
Once the steak is cooked, toss it with the veggies and add the butter from the small pot.
Serve the steak and veggie mixture on a plate. Pour the cowboy butter sauce into a small dipping bowl. Enjoy dipping the steak tips into the golden butter sauce!