Halve the chicken breasts lengthwise so you have 4 thin cutlets. Sprinkle both sides with salt, pepper, garlic powder, and smoked paprika.
Heat olive oil in a grill pan or skillet over medium-high. Add the chicken cutlets and cook for 4 to 5 minutes per side, or until browned and cooked through. In the last minute of cooking, brush both sides generously with BBQ sauce and let the sauce caramelize.
Preheat your broiler or toaster oven. Place each cooked chicken cutlet on the bottom half of a sandwich roll. Spoon extra BBQ sauce on top, then add a slice of mozzarella cheese. Leave sandwiches open-faced and place under the broiler for 1 to 2 minutes, just until the cheese is melted, bubbly, and starting to turn golden.
Sprinkle with dried parsley if you like. Close up your sandwiches and serve immediately with a side of chips, fries, or fresh salad.
Notes
Leftover sandwiches will keep in the fridge for up to 3 days. For best taste, store the chicken, buns, and cheese separately if possible.