Dice tomatoes into 1-inch chunks. Halve cucumbers lengthwise, then slice into half-moons about 1/4-inch thick. Thinly slice red onion into rings or half-rings. Chop parsley and mint leaves.
In a small bowl, whisk together olive oil, red wine vinegar, Dijon mustard, minced garlic, salt, and pepper until emulsified.
In a large bowl, gently toss tomatoes, cucumbers, red onion, parsley, and mint with the dressing.
If using, fold in pita chips or croutons just before serving to keep them crispy.
Serve immediately or let rest for 10 minutes for flavors to meld. Garnish with extra herbs if desired.