Start by marinating your pork. Slice in thin medallions about ⅛-1/4 inch thick. Place in a bowl.
Combine remaining ingredients for pork marinade- fish sauce, honey, granulated sugar, black pepper and garlic. Mix well and pour over the pork. I like to mix in the marinade with my hands to ensure it is well mixed, massaging into each piece. Cover with saran wrap and set aside. You can marinate it anywhere from 1 hour to 7 hours. If it is only an hour, leave it on the counter top. If it will be longer, place in the fridge and bring to room temp before cooking.
While it is marinating, start the pickled veggies. Add radishes and carrots to a quart mason jar or bowl. Mix pickling solution in a separate container- the rice vinegar, sugar and salt. Pour over the veggies and mix well. Set aside to marinate while the pork is marinating.
Once the pork is ready to go, you have 2 options. You can either grill it, which is yummy. Or you can skillet fry it, which is really yummy too! If you are skillet frying, heat your cast iron pan on medium until it is hot. Add the oil and heat this as well. Lay the pieces of tenderloin on the pan. There is so much pork you will need to do this in several batches. Now, fry for about 3 minutes per side. It won't take long. Quickly, and carefully wipe down the pan if needed and start again until all the pork is cooked.
Now it's time to assemble the sandwiches.
If you are using the sriracha mayo, which I recommend, slather that on the bottom bun. Next add on your pork tenderloin. Top that with plenty of the pickled veggies. Cilantro and cucumbers are last. Then slather on more mayo on the top of the bun, and place that on. You are ready to go.