Thinly slice the onion and collect it in a small pot. Add the olive oil, some crushed chili pepper and a good pinch of salt. The salt will help you stew the onions without burning it, as it will extract moisture from the onions.

Stew the onions on low flame until soft and translucent, for about 5-8 minutes.

Break down the canned tuna chunks with a fork and add it to the onions.

Cook the tuna with the onions for a couple of minutes, stirring often, then add the tomato purée. Stir well, season with salt, then cook on the lowest flame for about 10 minutes, until thick and shiny. Set aside.

Put a large pot of water on the stove and bring it to a boil. When the water is boiling, salt the water and add the pasta. Stir and cook following the packaging time until al dente.