Preheat the oven to 375°. Using a food processor, coarsely grind the oats; transfer to a large bowl. Add the onion to the processor and finely chop.
In a medium skillet, heat the olive oil over medium heat. Add the onion and cook, stirring, until softened, about 5 minutes. Remove from the heat and let cool.
Puree the roasted peppers in the food processor; set aside 1/3 cup. Whisk the remaining roasted pepper puree into the oats along with the cooked onion, 6 tablespoons parmesan, the parsley, egg and egg white, 1 1/2 teaspoons salt and 1/2 teaspoon pepper. Crumble the ground beef into the bowl and stir to combine.
Transfer the meat mixture to a 5-by-9-inch loaf pan; spread the reserved roasted pepper puree on top. Bake for 50 minutes, sprinkle with the remaining 2 tablespoons parmesan and bake for 5 minutes more. Let stand for 10 minutes before slicing.