Place cereal mix in the bowl of a large stand mixer. Pour boiling water over top and gently stir. Let stand at room temperature until mixture reaches 110F, about 30 minutes.
Dissolve yeast into slightly-warm water mixture. Let stand for 5 minutes then mix in oil, honey, egg, and salt. With mixer on low speed, add rye flour, oats, sunflower seeds, chia seeds, and 4-1/2 cups flour. Increase speed to medium and mix until dough pulls away from sides. If needed, add more flour by the tablespoon until dough is smooth and not at all sticky.
Turn dough onto a floured surface and gently knead until smooth and elastic. Place dough in a greased bowl, turning once to grease top. Cover bowl with plastic wrap and let rise in a warm place until doubled, about 1-1/2 hours.
Punch risen dough down and divide in half. On a floured surface, use your hands to stretch each portion of dough into a 9x5 rectangle. Roll into a cylinder-shape along the length side and pinch edges to seal. Tuck ends underneath and transfer dough loaves to two greased 9x5 loaf pans.
Brush loaves with egg white and sprinkle with additional rolled oats. Cover pans with plastic wrap and let rise in a warm place until doubled, about 30 minutes.
Bake loaves at 375F 35-40 minutes or until a deep golden brown on the outside. Cool bread in pan 10 minutes, then transfer to a wire cooling rack to cool completely.
Store bread in an airtight container at room temperature up to 4 days. Bread may also be frozen up to 1 month.