Fennel and Celery Salad

Ingredients: 3 stalks celery, thinly sliced on the diagonal 1 fennel bulb – trimmed, cored and thinly sliced 1/3 red onion, thinly sliced 1 tablespoon chopped fresh parsley 1 lemon, juiced 2 tablespoons olive oil, or more to taste salt and ground black pepper to taste