Bring a large pot of salted water to a boil. While water boils, add 2 tablespoons oil and panko to a large saucepan over medium heat. Stir to coat panko with oil and sauté for 5 minutes, shaking pan occasionally to ensure even browning. Pour toasted panko into a small bowl and set aside.
Add remaining oil and onions to the pan and sauté over medium heat until lightly browned, about 7 minutes. Turn off heat. Add crème fraîche, lemon zest and juice and stir gently to combine.
While onions are cooking, add pasta to boiling water. Boil 4 minutes, stirring occasionally. Add peas and boil another 4-5 minutes. Drain pasta and add to crème fraîche mixture. Turn heat to high and stir until pasta is well coated and sauce thickens, about 2 minutes.
Turn off heat and add Parmesan to pan, stirring to coat pasta. Season with salt & pepper, to taste. Ladle pasta into bowls, top with toasted panko and serve immediately.