Spray a loaf pan with nonstick spray and line it with parchment paper.

In the bowl of a stand mixer, whisk together the water, honey, and yeast. Set aside for 5 minutes. The mixture should be frothy and smell like yeast.

Attach the bowl to the mixer with the paddle attachment. Add in the psyllium husks, egg, and olive oil. Mix on medium speed until incorporated. Turn off the mixer and let the mixture sit for 5 minutes to thicken.

Add in the buckwheat flour, brown rice flour, baking powder, and salt. Mix on medium until everything is well combined. Pour the mixture (it will be thick) into the prepared pan. With wet hands, smooth the top into an even layer. Cover with a towel and let rise for 45 minutes in a cool draft-free place. The bread should double in size.

While the bread is rising, preheat the oven to 350 degrees. Once risen, gently remove the towel and transfer to the oven. Bake for 45-55 minutes or until the bread is golden brown and when tapped, sounds hallow. Let cool for 5 minutes in the pan, transfer to a wire rack, and let cool before slicing.