Roasting garlic scapes with tomatoes and red onion sweetens them and enriches their flavor; toss them with pasta, lemon juice, and arugula for a simple summer meal.
Heat oven to 400°. Bring a large pot of salted water to a boil; add spaghetti and cook, stirring occasionally, until al dente, about 8 minutes. Drain pasta and keep warm. Toss olive oil, garlic scapes, tomatoes, red onion, salt, and pepper and spread in an even layer on a baking sheet. Roast for 12–15 minutes, until tomatoes are just beginning to burst. Remove from oven and toss with spaghetti, arugula, and lemon zest and juice. Serve immediately.