2 days before making granola, crumble feta finely onto a plate, spreading out the cheese as much as possible. Refrigerate it, uncovered, for 48 hours so that it dries.
Preheat the oven to 325 degrees.
Cut a piece of parchment paper to just fit onto a baking sheet, then lightly grease the parchment with a few drops of oil.
In a large mixing bowl, combine oats, salt, pimentón, and cumin, stirring well. Scatter the seasoned oats evenly over the parchment, then drizzle with the remaining olive oil.
Bake for 10 minutes, then remove the sheet from the oven and set it aside until the oats are cool enough to handle. With your hands, mix in the pine nuts, almonds, sun-dried tomatoes, and chile flakes if using, then spread the granola out evenly again on the parchment and return it to the oven.
Bake for 10 minutes more, then remove the sheet from the oven again and allow the granola to cool. With your hands, mix in the dried feta. Serve on top of plain Greek yogurt.