Preheat the oven to 350 degrees F.
Place the Gala apple, green apple, sweet onion, and sea salt onto a small sheet pan or oven safe skillet.
Roast for 20 minutes.
Pour the olive oil over the apples and onions. Reduce the oven temperature to 300 degrees F and continue roasting for another 20 minutes until everything is very soft.
Allow the apples to cool slightly. Scrape the softened apple flesh away from the skins and discard the skins.
Transfer the roasted apple flesh and onions to a blender or food processor. Pulse until mostly smooth with a slight texture.
Transfer the mixture to a mixing bowl.
Whisk in the Dijon mustard, Parmesan cheese, Italian seasoning, dried dill, and black pepper.
Slowly whisk in the apple cider vinegar until fully incorporated.
Taste and season with additional sea salt if needed.
Serve immediately or refrigerate until chilled.