Preheat the oven to 300 degrees F and lightly oil a rimmed baking sheet.
In a large mixing bowl, combine the oats (both kinds), buckwheat, walnut pieces, sunflower seeds, rosemary, and salt. In a small bowl, beat the egg white very briefly, until it begins to froth, and then stir in the olive oil and maple syrup. Add this to the oat mixture, stirring it well, until everything is well-coated.
Spread evenly on the baking sheet and bake for about 40 minutes, rotating the pan halfway through, or until the granola is lightly golden. (If you want more clumps of granola, do not stir; if you want no clumps, stir every 10 to 15 minutes.) Remove from the oven and let cool completely on the baking sheet. Store in an airtight container.