Not sure who you are going to give the other sandwich to, but they are going to really like you!
In a large skillet, melt 1 tablespoon butter and add onion. Cook over medium-high heat until onions start to caramelize.
While onions are cooking, melt the Smoked Gouda cheese with heavy cream in a small saucepan, stirring quickly and often, until smooth. Remove from heat and set aside.
Spread remaining 2 tablespoons butter over steak rolls and place under broiler just until they start to brown.
Layer half of roast beef over bottom side of each steak roll and top with caramelized onions. Drizzle barbecue sauce evenly over roast beef and onions. Pour half of cheese sauce over barbecue sauce, layer on avocado slices and sprinkle with garlic salt. Add the tops of the steak rolls.