Rinse all vegetables under cold water and dry thoroughly using a salad spinner or clean towels.
Thinly slice the celery on a diagonal, chop the herbs and celery leaves, slice the red onion, and halve the cherry tomatoes.
Add the celery, tomatoes, herbs, celery leaves, and red onion to a large mixing bowl and toss gently.
In a small jar or bowl, combine olive oil, lemon juice, lemon zest, Dijon mustard, oregano, chopped olives, feta, and grated garlic, then shake or whisk until emulsified.
Pour the dressing over the salad and toss lightly until everything is evenly coated.
Season with freshly ground black pepper and garnish with extra kalamata olives and feta if desired.
