In a medium bowl, combine mayonnaise, buttermilk, garlic and onion powder, paprika, cayenne pepper, black pepper, and ranch dressing mix.
Whisk until well combined. Refrigerate until ready to use.
Preheat the oven to 400°F.
Cut bread into bite sized squares and spread on a sheet pan. Bake 12-16 minutes or until the bread is slightly browned.
Meanwhile, in a small bowl, mix together butter, cajun seasoning, and garlic.
Carefully remove the sheet pan from the oven and lower the temperature to 350°F. Pour the melted butter mixture over the toasted croutons and toss until all of the pieces are coated well. Return the pan to the oven 6-8 minutes. Remove from the oven and cool.
In one large bowl or individual bowls, build the salad with lettuce, tomato, cucumber, red onion, cheddar cheese, Monterey Jack cheese, and croutons.
Toss or top with desired amount of dressing.
