Prep and chop red onion, cucumbers, celery, bell pepper, and scallion.
Combined the chopped vegetables, drained tuna, lemon juice, olive oil, dijon mustard, gochugaru, and ground black pepper.
Mix together well until thoroughly combined. Taste and adjust for seasoning if desired.
Toast the bread in a toaster or in a pan over the stove top. Be careful not to over-toast them otherwise, they will be too crunchy!
Remove the bread onto a plate and carefully rub the garlic cloves on both sides.
Serve and enjoy!