In a large non-stick skillet over medium heat, soften the onions in the oil until they begin to brown. Add the fish and lemon juice. Continue cooking for about 5 minutes or until the fish is cooked and flakes easily. Add the garlic and red pepper flakes. Continue cooking for 1 minute. Season with salt and pepper.
Meanwhile, in a large pot of salted boiling water, cook the spaghetti al dente. Reserve 1 cup (250 ml) of the cooking water. Drain.
In the skillet, add the spaghetti, ½ cup (125 ml) of the cooking water, the cilantro and lemon zest to the fish mixture. Toss gently. Add cooking water or oil if needed. Adjust the seasoning.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.