Lightly grease a 7 by 4 by 3-inch loaf pan with oil.
In a small bowl, combine the coconut oil, warm water, agave nectar, and yeast. Stir once and set aside until it bubbles, about 10 minutes.
In a large mixing bowl, whisk together the potato starch, flours, arrowroot, baking powder, xanthan gum, and salt. Add the yeast mixture and, using a rubber spatula, stir until it is the consistency of a cake batter. Add more warm water one splash at a time if the batter is too thick. Pour the batter into the prepared loaf pan, cover with a dishtowel, and let rise for 1 hour.
Preheat the oven to 400°F.
Bake the bread for 20 minutes. Rotate the pan 180 degrees and bake until the crust is golden and a toothpick inserted in the center comes out clean, about 15 minutes. Let the bread cool in the pan for 1 hour before slicing.