Preheat your oven to 350°F and prepare a large baking sheet for the bread.
Cut the bread into a grid pattern by slicing it 3/4 inch thick, careful not to slice through to the bottom.
Mix the melted butter, cheddar cheese, parmesan cheese, minced garlic, and a bit of salt in a bowl.
Spread the cheese mixture between the cuts in the bread, ensuring it seeps down to the bottom.
Wrap the loaf in foil and bake on the prepared sheet for about 15 minutes.
Unwrap the foil, top with chopped green onion, and bake for an additional 5 minutes.