Trim the asparagus and cut off the woody part of the stalks. Cut off the tips and slice the rest into rounds. Heat the olive oil in a large frying pan and add the onion. When the onion begins to soften, add the asparagus rounds. Pour over ½ cup (120 ml) water and season to taste with salt. Cook for 10 minutes over medium heat. Remove from the heat, puree with an immersion blender or in a food processor and set aside.
Bring a large pot of salted water to a boil. Add the pasta and the asparagus tips and cook for about 3 minutes. Drain and transfer to the asparagus puree. Toss to coat and crumble over the tuna. Mix carefully and serve immediately.

Delicious and Healthy
Asparagus are very versatile in the kitchen. From a nutritional perspective they provide essential vitamins and minerals (calcium and phosphorus in particular), and are low in fat and calories.