Heat the olive oil in a skillet over medium heat. Add the garlic, onion, and green pepper. Cook the vegetables for about 5 minutes or until the start to get tender, making sure to stir them so they don't burn. Once the vegetables are tender add the spinach and continue to cook until the spinach is wilted and reduced down. Remove from the heat and allow to cool completely.
Once the spinach mixture is cooled put into a food processor and process until smooth. I used a mini processor works well.
In a small to medium bowl add the sour cream, dressing/mayonnaise and spinach mixture mix until well blended. Add the celery salt and mix in. Season with additional salt and pepper to taste.
It is good to refrigerate for an hour or more to let the flavors blend together.