Blanch the asparagus by cooking them in boiling salt water for 4 – 5 minutes. Remove from the heat and place in ice-cold water. In a pot, heat a little olive oil, and cook the onions until they turn translucent. Add the asparagus, the hot stock and cook for a few minutes. Remove the pot from the heat and with a hand blender, mash the asparagus until smooth. Return to the heat, season with salt and pepper, and cook just enough to heat through. Serve the slices of tuna with a drizzle of soya and a generous amount of asparagus mousse. Bon Appétit!