In a large bowl, combine the drained tuna, cherry tomatoes, cucumber, red onion, bell pepper, olives, capers (if using), and parsley. Gently toss to mix.

In a small bowl, whisk together the olive oil, lemon juice, Dijon mustard, minced garlic, salt, and pepper until the dressing is well blended.

Pour the dressing over the salad ingredients and toss gently until everything is evenly coated.

Taste and adjust seasoning as needed. Serve immediately or chill briefly for a cooler, more melded flavor.