Combine the tuna, celery, red onion
, Dijon, anchovy paste, lemon juice, pepper, salt, and oregano
in a medium bowl and stir until thoroughly combined.
Preheat a nonstick pan over medium heat.
two pieces of the bread with half of the tuna
mixture, half of the sliced tomatoes
, if using, and half of the cheese. Cover with two additional slices of bread.
Add half of the butter
and half of the olive oil
to a hot pan. When hot, add 2 sandwiches and cook until browned on both sides, about 2 minutes each side. Repeat with the remaining bread and tuna mixture. Serve hot, with a side salad of hearts of palm
, tomato, and torn fresh basil leaves, if desired.