Set a large pot of salted water to boil. In a wide pot or large pan, cook bacon over medium, stirring occasionally, until crisp. With a slotted spoon, scoop out the bacon onto a paper towel-lined plate to drain. Pour the rendered fat into a bowl and reserve. Add back 2 tablespoons of the drippings to the pan. Add leeks, sprinkle with salt and pepper and cook, stirring often, until leeks are soft and golden brown, about 5-7 minutes. Sprinkle with the crushed red pepper flakes. Add back the cooked bacon, as well as the peas, just to warm them through, then turn off the heat.

Meanwhile, while the leeks are cooking, add pasta to the pot of boiling water and cook according to package instructions. Scoop out ¼ cup of the starchy salted cooking water and reserve. While you’re waiting for your pasta, in a small bowl, whisk together eggs, Parmesan cheese, lemon zest, and lemon juice.

Drain pasta and immediately add to the bacon, leeks, and peas, along with the reserved cooking water. Add another tablespoon of reserved bacon drippings to the pasta. Make sure your pan is off the heat, and add egg mixture, while stirring vigorously with the hot pasta. Stir quickly so the eggs don’t scramble. Fold in the arugula and let the warmth of the pasta wilt it slightly. Season with salt and pepper if necessary. Sprinkle with more cheese if desired and serve immediately.