Macerate the garlic: In a small bowl, combine the lemon juice and the minced garlic; let sit 10 minutes to mellow the sharpness.
Make the dressing: Whisk in Dijon, oregano, pepper, and salt. Slowly drizzle in the olive oil, whisking until emulsified.
Prep the brined items (optional but recommended for lower sodium): Briefly rinse and pat dry the olives, capers, artichokes, and roasted peppers.
Combine the salad: In a large bowl, add the drained, flaked tuna, artichokes, olives, red onion, cucumber, roasted peppers, capers, dill, mint, and green onions.
Dress & toss: Pour the dressing over the salad and toss gently until evenly coated. Adjust salt/pepper to taste.
Chill: Cover and refrigerate 20–30 minutes for flavors to marry.
Serve: Spoon into lettuce cups, pita, or enjoy as is.