Turn broiler in the oven on Low.Wash and Slice the Red Pepper in four slicesPlace the Spinach leaves onto the Red Pepper wedges and sprinkle with onion powder. Drain the tuna and place it in a small bowl. Add the onion, celery, sunflower seeds, mustard, and mayo and mix well. Divide the tuna mixture over the four red pepper wedges and cover each with 1/2 slice of cheese (cut in fourths). Place in a dish under the broiler until the cheese melts, just a couple of minutes. Top the pepper slices with fresh dill and enjoy!