In a large mixing bowl, whisk together the all-purpose flour, salt, and instant yeast until well combined.
Add the warm water to the dry ingredients and stir with a wooden spoon or spatula until a shaggy dough forms. The dough will be sticky and rough; do not knead.
Fold in the shredded sharp cheddar cheese and shredded mozzarella cheese until evenly distributed throughout the dough.
Cover the bowl tightly with plastic wrap or a clean kitchen towel and let the dough rest at room temperature for 12 to 18 hours, or until the surface is dotted with bubbles and the dough has doubled in size.
After the dough has risen, preheat your oven to 450°F (230°C). Place a heavy Dutch oven or oven-safe pot with a lid inside the oven to heat for 30 minutes.
While the oven and pot are heating, lightly flour a clean surface and turn the dough out onto it. Using floured hands, gently shape the dough into a round loaf by folding the edges toward the center. Avoid deflating the dough.
Sprinkle the garlic powder over the dough and drizzle the olive oil on top, gently pressing it into the surface.
Carefully remove the hot Dutch oven from the oven. Place the dough into the pot and cover it with the lid.
Bake the bread covered for 30 minutes. Then remove the lid and bake for an additional 15 minutes, or until the crust is deep golden brown and crisp.
Remove the bread from the oven and transfer it to a wire rack. Let it cool completely before slicing.