Mash the avocados with the lime juice and add salt to taste. Arrange the rolls open on plates and spread the avocado mixture on the roll tops.
In a large nonstick skillet, cook 3 portions of steak over medium-high heat, seasoning lightly with the chili powder, for 1 minute. Flip the meat, sprinkle with some cheese and push off to the side of the pan. Continue adding meat, chili powder and cheese to the skillet until all of the meat is cooked and topped with cheese.
Place a few tomato slices on each roll bottom. Divide the steak among the 4 sandwiches and sprinkle with hot pepper sauce, if using. Set the roll tops into place.