Preheat your oven to 425°F (220°C).
Ensure the rack is set in the middle position.
Slice the French loaf in half lengthwise.
Then, cut each half so you have manageable pieces.
In a bowl, mix the cheddar, Monterey Jack, Parmesan, mayonnaise, and green onions.
Add a dash of salt to taste.
Melt butter in a skillet over medium heat.
Add garlic and sauté until fragrant for about a minute.
Spread the cheese mix generously over each bread piece.
Bake in preheated oven for 10 to 12 minutes or until cheese is bubbly and slightly golden.