Start by rinsing all your vegetables under cold water. Pat them dry with a kitchen towel or use a salad spinner for quick drying.
Peel the celery if desired, then slice it thinly on a diagonal.
Slice the cherry tomatoes in half and peel the red onion before slicing it thinly.
Chop the fresh parsley and basil, and add them to the large mixing bowl with celery, tomatoes, and onions.
In a separate bowl or mason jar, mix together olive oil, lemon juice, grated lemon zest, Dijon mustard, dried oregano, chopped kalamata olives, feta cheese, and grated garlic. Whisk or shake until well combined.
Pour the dressing over the salad mixture in the large bowl and toss everything together gently but thoroughly.
Season with freshly ground black pepper to taste and serve immediately or let it sit for about 10 minutes to allow flavors to meld.