Finely chop the cabbage and put in a deep bowl. Also finely chop the green bell pepper and cucumber, add to the bowl. Add finely chopped dill and chopped celery stalks.
Mix olive oil, lemon juice and Dijon mustard in a bowl. Pour dressing into a bowl of vegetables, add salt and pepper.
Mix everything thoroughly and cover the salad with a lid, let it sit for 5 minutes to marinate a bit, then mix again and serve.