These juicy, tender tri-tip steak sandwiches are topped with heavenly melted cheese and a generous dollop of chimichurri and horseradish sauce. Whether you have leftover tri-tip that you need to use or if you are craving a delicious sandwich packed full of flavor, this sandwich will be sure to hit the spot There is a lot to love about this delicious recipe, including its tender meaty center, the toasted ciabatta rolls, and the combination of herby chimichurri and creamy horseradish that give the entire sandwich a well-rounded flavor. I like to assemble this sandwich on the Blackstone after carmelizing the onions to perfection. The flat top griddle is a great work surface, making it incredibly easy to toast the ciabatta buns and melt the provolone cheese for that photo-worthy gooey cheese.