Cook the pasta in salted water until tender, timing it so that it is still quite warm when everything else is ready.
Place the crumbled feta in a medium bowl. Gather the arugula into a rough bundle and run your knife through it a few times to create strips. Place the strips in the bowl with the feta.
Once you’re basically ready to assemble, heat the olive oil in a small skillet over medium heat. Add the sliced onion and salt. Cook until the onion is translucent–it’s okay if it browns in a few spots. Remove from the heat and add the lemon zest, juice, and ground chile.
Drain and add the hot pasta to the bowl with the arugula. Drizzle with the hot olive oil/onion mix. Using tongs, toss until everything is well combined. Taste and add more salt if needed. Eat warm or let cool to room temperature before serving.
Notes
Onion Alternatives: Spring onions are a favorite of mine thanks to their slightly mellow onion flavor. However, you can easily swap an allium. Go with garlic (or green garlic), shallot, scallions, or minced yellow onion.Ground Chile: I really adore Diaspora Co’s Guntur Sannam Chilli when I reference medium-heat ground chile. However, if you have a ground chile you prefer- go with it! You can swap the ground chile for ground black pepper if heat isn't your thing. No Wilted Greens: If you prefer your arugula to maintain the fresh green quality, let the pasta and oil cool before tossing everything together.Lemon: If you have preserved lemons on hand, you can swap out the zest/juice for the preserved lemon. I like to add a teaspoon or so of rice vinegar to the preserved lemon to give it a bit of zing as well.