Spray the inside of a slow cooker with nonstick spray.
Add the oyster crackers, ranch seasoning, garlic, dill, and vegetable oil. Stir to completely combine.
Cover and cook on low heat for 1 hour. Stir every 20 minutes to ensure even cooking.
After 1 hour, add the butter until it is melted around 5 minutes. Stir to coat the crackers.
Turn off the slow cooker. Add the parmesan cheese and stir to incorporate.
Remove the crackers from the slow cooker. Serve with freshly chopped parsley.