Put all the ingredients in your slow cooker and give everything a good mix so that all the seasonings are distributed as evenly as possible. Cover with lid and cook on HIGH for 1-1.5 hours or on LOW for 2-3 hours.
Serve warm! Best served right away or when kept on WARM in your slow cooker.
Notes
You can use less spinach or slightly increase it to 2 cups (which is about 2 ounces of fresh spinach). Adding more than that would make this dip very thick so you might need to add extra yogurt.
Greek yogurt can be substituted with natural yogurt or sour cream.
The number of servings can vary. This will depend on many factors: whether you will be serving other appetizers/snacks at your party, how long your party will last but most importantly while I can enjoy only a teaspoon of this dip on my cracker you might enjoy a full tablespoon. For this reason, take the serving number as a guide only. I counted with a ⅓ cup of dip per person.
I cook this on HIGH for 1 hour (if 1 hour does not seem to be enough add an extra 30 minutes. It should not need more than this.) You can cook it on LOW for 2-3 hours (check if the dip is warm and the cheese is melted).