Preheat oven to 325 degrees F. Season the pork with salt and pepper and brush with 1 cup of the bbq sauce, place in a medium saucepan. Pour the stock over and bring to a simmer on top of the stove. Cover and place in the oven to braise for 1 hour, or until cooked through. Remove from the cooking liquid. Bring the cooking liquid to a boil on top of the stove and reduce by half. Preheat a grill pan until almost smoking. Add the pork, brush with the reserved bbq sauce and grill for 2 to 3 minutes on each side or until a crust forms. Remove, let rest and slice on the bias into 1/4-inch slices. Lay the tortillas on a flat surface. Place 1 tablespoon of each cheese over 1 side of each tortilla. Place a few slices of onion over the cheese, then 3 to 4 slices of potatoes. Add the sliced pork to the cooking liquid to moisten then place 3 to 4 slices of pork on top of the cheese, place a little more of the cheese on top of the pork, then some of the cilantro. Fold the tortilla over and press down slightly. Brush the tops of the tortillas with some of the oil and place on a lightly oiled baking sheet. Bake in a 350 degree oven until the tortillas are lightly golden brown and the cheese has melted, 5 to 7 minutes.
Tomatillo-Roasted Red Pepper Relish:
Combine all ingredients in a medium bowl. Let rest at room temperature for 30 minutes.
Smoked Red Pepper Sauce:
In a blender, combine the peppers, onion, chipotle and lime juice and blend until smooth. With the blender running, add the olive oil in a thin stream until the sauce is emulsified. Season to taste.
Smoked Yellow Pepper Sauce:
In a blender, combine the peppers, onion, chipotle and lime juice and blend until smooth. With the blender running, add the olive oil in a thin stream until the sauce is emulsified. Add the sugar and salt and pepper to taste.