Preheat oven to 325 degrees F (165 degrees C).

Mix butter, Parmesan cheese, oregano, thyme, garlic powder, and salt together in a large, flat-bottomed bowl; add bread cubes and turn with a spatula to coat. Spread coated bread cubes onto a baking sheet.

Bake in preheated oven until golden brown, 15 to 20 minutes. Cool croutons completely before storing in an airtight container.