1) Combine all of the ingredients, and mix until cohesive. Cover the bowl, and let the dough rest for 20 minutes, to give the whole grains a chance to absorb some of the liquid. Then knead — by hand, stand mixer, or bread machine — to make a smooth, soft, elastic dough.
2) Place the dough in a lightly greased bowl, or in an 8-cup measure (so you can track its progress as it rises), and let it rise for 1 to 1 1/2 hours, until it's risen noticeably. It won't necessarily double in bulk.
3) Gently deflate the dough, and divide it into 12 pieces (about 70g each). Shape each piece into a round ball; use your fingers to pull and flatten each ball into a circle about 3" across.
4) Place the buns on a lightly greased or parchment-lined baking sheet, cover, and let rise for about 90 minutes, until noticeably puffy. Towards the end of the rising time, preheat the oven to 350°F.
5) Brush the buns with the egg white/water mixture. Sprinkle with oats and/or flax seeds.
6) Bake the buns for 21 to 25 minutes, until they're golden brown. Remove them from the oven, and transfer them to a rack to cool.
7) Wrap completely cooled buns airtight, and store at room temperature for several days; freeze for longer storage.
Yield: 12 buns.