Heat the olive oil in a large skillet over medium-high heat until it shimmers and moves easily when you tilt the pan, about 1-2 minutes.

Add the sliced steak to the skillet in a single layer and season generously with salt and pepper. Cook without moving for 2-3 minutes to develop a nice crust, then flip and cook another 2-3 minutes until browned with some pink remaining. Remove the steak from the skillet and set aside.

In the same skillet, add the sliced bell peppers and onions. If using mushrooms, add them now too. Sauté for 5-7 minutes, stirring occasionally, until they soften and develop golden-brown edges.

Add the minced garlic and cook for 1 minute until fragrant.

Return the cooked steak to the skillet with the vegetables and toss everything together. Sprinkle the cheese over the top, cover the skillet, and cook for 2-3 minutes until the cheese melts completely.

Remove from heat and divide among bowls. Serve immediately with optional toppings like mushrooms, jalapeños, or fresh parsley.