Preheat oven to 350 degrees F.

Line a baking sheet with two sheets of aluminum foil, positioning one lengthwise and the other widthwise to create a cross shape.

Cover the foil with a piece of parchment paper and set the baking sheet aside.

Grate the mozzarella and cheddar cheese and set them aside. (You can save time by using pre-shredded cheese).

Chop the green onion and set it aside.

Finely dice the two cloves of garlic and place them in a saucepan.

Add the stick of unsalted butter, salt, pepper, and red pepper flakes to the saucepan.

Put the saucepan on the stovetop and heat over medium heat until the butter just melts. Stir the mixture with a whisk, spoon, or fork, and set it aside while you prepare the bread.

Position your loaf of bread on a cutting board and cut it diagonally, going about ¾ of the way through the loaf without completely separating the slices. Make cuts about 1 inch apart.

After cutting diagonally in one direction, repeat the process in the opposite direction, creating 1-inch sections of bread that are still attached to the loaf.

Place the loaf on the prepared baking sheet (with the foil and parchment paper).

Using a spoon or pastry brush, evenly distribute the butter mixture so that the butter and garlic get into each of the cuts (or slices).

Sprinkle the shredded cheddar cheese evenly over the cuts (or slices) and press it inside the bread loaf. Repeat this step with the mozzarella cheese.

Top the loaf with half of the sliced green onions.

Close up the bread by bringing together the parchment paper and then one piece of foil. Secure the other piece of foil to cover the entire loaf.