In a small bowl, pour 3 tablespoons boiling water over millet and let stand 15 minutes.
In another bowl, pour remaining boiling water over chia and stir until a thick paste forms.
In a third bowl, whisk together warm water, yeast, and sugar and let stand until foamy, 10 minutes.
In the bowl of a standing mixer, whisk together flours, starches, seeds, and salt. Add drained millet, chia and yeast mixtures, eggs, and honey, and, with the paddle attachment, mix on low speed for 30 seconds. Turn mixer to high speed and mix for 1 minute.
Brush loaf pan with oil and transfer dough to pan. Dust with rice flour and loosely cover with plastic wrap. Let loaf rise until doubled in volume, 45 to 60 minutes. Meanwhile, heat oven to 400 degrees.
Bake loaf for 10 minutes, then reduce heat to 350 degrees and bake until golden brown and a toothpick inserted in center comes out clean, about 30 minutes more.
Cool bread 15 minutes in pan, then transfer to a wire rack to cool completely.
Wrapped in parchment, bread keeps at room temperature two days; wrapped in foil, it will keep in the freezer up to one month.