- Cook the pasta in boiling salted water until al dente. Reserve 125 ml (1/2 cup) of the cooking water. Drain and set aside.
- In a large skillet, brown the onions in the oil until tender. Season with salt and pepper. Add the tuna, tomatoes, olives and garlic.
- Sauté for about 2 minutes. Add the pasta, parsley, and lemon zest and juice. Stir well and heat until warm, adding some of the reserved cooking water if necessary. Adjust the seasoning.