California Tri Tip Sandwich.
First, you take a nice Dutch Crunch (Or French, or whatever you prefer.) sandwich roll, and you split it with a knife (but not all the way through.)
Then, you take a Tri-Tip cut of cow. (We call it Tri-Tip in California. You may know the cut as a "Santa Maria Steak" in other parts of the US, or as a "Triangle Steak" in the UK.) Marinate it how you wish and barbecue it to whatever level of cooked you prefer. I like to marinate in Worcestershire sauce and then baste it with barbecue sauce in the last few minutes of cooking.
Slice the steak as thin as you can. Spread a little honey Dijon mustard (Or mayonnaise. Really, it's all personal preference.), on the roll and layer the steak slices in a kind of crumpled, folded pattern. Add cheese to the top (I like a medium cheddar, but swiss, jack, or any other hard cheese you prefer works well.) and stick it in the oven at about 425 degrees until it's toasted and the cheese is melted.
Sandwich perfection.
Of course, other ingredients added to the sandwich allows you to customize it. Avocado works very, very, VERY well, as well as shredded lettuce, sprouts, tomato, onion, green peppers, etc.
The Tri Tip is a delicious, and often overlooked cut of beef.