Cut the pork tenderloin crosswise into 4 even pieces. Pound the pork slices evenly with a mallet or rolling pin to 1/4-inch thick. Lightly season the pork on both sides with salt & pepper.
Setup 3 shallow bowls: Mix the flour, garlic powder, 1 tsp salt, and 1/2 tsp pepper in the first bowl. Beat the egg in the second bowl. Add the breadcrumbs to the third bowl.
Working with one slice of pork at a time: Place a slice of pork in the flour mixture and flip to coat. Shake off any excess flour then dip the pork into the beaten egg and flip to coat. Shake off any excess egg then place in the breadcrumbs, flip and lightly press the breadcrumbs onto the pork to help adhere. Shake off any excess breadcrumbs then place the breaded pork on a plate and set aside, continue with the remaining pork slices.
Heat the oil over medium heat in a large skillet or cast-iron pan.
When the oil is hot, working in batches, fry the pork in the hot oil until lightly browned, about 2 minutes then flip and fry for 2 more minutes. Transfer the cooked pork to a paper towel lined plate and continue with the remaining pork adding more oil if necessary.
Serve the pork on the buns with lettuce, pickles, and mayo.