Preheat oven to 450°F.
In a small saucepan, add potatoes, cover with cold water and bring to a boil. Cook until the potatoes are completely cooked through, 10-12 minutes. Drain and allow to cool slightly.
While still warm, mash the potatoes and add the ricotta, tuna, parsley, lemon zest, egg yolk, salt and pepper. Add the egg yolks and mix to combine.
Fill each piquillo pepper with about 2 teaspoons of filling and place stuffed peppers in an oiled baking dish. Drizzle a little more extra virgin olive oil over the top and bake for 10 - 15 minutes, or until warmed through. Serve hot.