Spray your slow cooker with non-stick cooking spray or line with parchment paper for easy cleanup.
In a large bowl, combine melted butter, minced garlic, Italian seasoning, and salt. Mix well.
Add bread cubes to the bowl and toss until evenly coated with the butter mixture.
Transfer half of the bread cubes to the slow cooker, then sprinkle with half of the Parmesan and mozzarella. Repeat with remaining bread and cheese.
Cover and cook on LOW for 2 hours, stirring gently halfway through to prevent sticking.
Garnish with fresh parsley and serve warm. Keep on the "warm" setting during your party.