Drain the tin of tuna well in a sieve so that as little liquid as possible remains. Rinse the celery stalk and cut it with a sharp knife into very fine pieces. Rinse the large red bell pepper, cut it lengthwise in half and carefully remove the white membranes and seeds. Cut or chop the fresh chives into small rings.
Place the drained tuna in a large bowl and gently pull apart the pieces of fish with a fork. Add the tablespoon of organic mayonnaise, the finely chopped celery and the cut chives to the tuna. Mix everything together thoroughly until a creamy and cohesive salad forms.
Place the two cleaned bell pepper halves cut-side up on a cutting board. Scoop the tuna salad into the peppers and distribute the filling evenly over both halves. Press the salad gently with the back of a spoon so the peppers are generously and compactly filled.
Transfer the filled pepper halves to a plate. Serve the dish immediately cold, or store covered in the refrigerator until you are ready to serve.