Put the first 9 ingredients into a blender and pulse for about 20 seconds.
Put the steak into a ziplock bag and pour the marinade in.
Place in the refrigerator for 4 hours or overnight.
Heat a grill and cook over high heat. The thinner the meat slices the shorter the cooking time. Very thin sliced beef will only need to cook a minute on each side.
Assemble the buns by cutting, placing them on a cookie sheet.
Layer a piece of cheese, some steak and top with a piece of cheese.
Leave the bun open and place in the oven at 375 for 3-5 minutes for the bun to toast and the cheese to melt.
Put a spoon of Pico de Galo and a spoonful of guacamole on top of the melted cheese. Close and secure with a pick.
Serve immediately or cover with aluminum foil to keep warm.