In a medium bowl, smash chickpeas with a fork until crumbly, and no full chickpeas remain. (This process can be done in a food processor, but be careful not to turn the mixture into a paste.)
Add celery, garlic, red onion, and olives. Stir until well combined. Add in olive oil and lemon juice, mixing until incorporated. Season with salt and pepper. Fold in feta and parsley.
Serve immediately or store in a Tupperware container for up to 5 days.
Notes
Marinated red bell peppers would make a great addition to this salad.