Peel potatoes and slice into fries. Rinse in cold water until water runs clear. Soak in cold water for 45 minutes.
Bring oil to 350. Fry potatoes in batches for about 8 minutes to cook through. Remove from oil and drain.
Bring oil to 450. Fry potatoes in batches for about 3 minutes to crisp and brown. Remove from oil and drain.
If using frozen french fries, cook according to package instructions.
Mix all the meat marinade ingredients with the steak in a large bowl. Allow to marinate for 45 minutes.
Mix all the pico ingredients and allow to sit in the fridge until ready to use.
Mash up the avocados, and add a scoop of pico to it. Season with salt and pepper and store in the fridge until ready to use.
Preheat oven to 350
Grill the steak on the grill or on a cast iron grill pan, about 6 minutes per side, to a medium doneness. Allow to rest at least 5 minutes before slicing the steak against the grain into thin strips.
Fill the taco shells with a few fries in each shell. Top with cheese. Bake the shells with the fries and cheese in them for 10 minutes.
Remove the shells from the oven. Top with steak, then add guac, pico, and sour cream. Serve.