1. In a large pot of salted boiling water, cook spaghetti until al dente. Keep 250 ml (1 cup) of cooking water when draining pasta. Lightly coat pasta with oil and set aside.
2. Meanwhile, in a large skillet, soften leek in oil. Add olives, capers and pepper flakes and cook for 2 minutes. Add tomatoes and simmer over low heat for about 5 minutes. Add tuna and stir.
3. Add pasta and toss well. Add a little cooking water, if needed. Season with salt and pepper.

NOTE FROM RICARDO

To save time, you can buy ready sliced leeks.