Preheat the oven to 400°F.
Lay the bread halves crust side down side by side on a baking pan.
In a mixing bowl, whisk together the softened butter, mayonnaise, minced garlic, garlic salt, and paprika until fully combined.
Mix the colby-jack and mozzarella cheese together. Reserve 1 cup.
By hand mix-in 2 cups of shredded cheese, grated Parmesan cheese and green onions into the butter mixture.
Divided evenly between the bread halves spreading from end to end. Sprinkle the reserved shredded cheese on top.
Bake at 400°F for 12 minutes, then increase the oven temperature to the broil setting.
Broil for 3 minutes or until golden and bubbly.
Slice into 1-inch strips, garnish with Italian parsley or chives. Serve immediately.