Bring a medium saucepan of salted water to a boil. Add celery stalks to the pot and cook until tender, 1 to 2 minutes. Drain celery and rinse with cold water to stop the cooking process.

Add red onion, garlic, lemon juice, red wine vinegar and a pinch of salt and pepper to a bowl, and stir. Let sit 2-3 minutes, until the onion softens. Add cooked celery stalks, celery leaves, red pepper, olives, and olive oil to the bowl and mix well. Chill in the refrigerator for an hour before serving. Season to taste with salt and pepper.