Cook the pasta and pre-heat the grill (broiler).
While the pasta is cooking, sift the flour into a saucepan and add the soya milk slowly, stirring constantly over a very low heat. Once all the flour is in, turn the heat up until the mixture bubbles. Add the stock cube/ bouillon and some of the water from the tin of asparagus (I add about 1/3, but it depends how thick you like your sauce). Then simmer for five minutes, stirring lots. Fold in the asparagus, and take the pan off the heat.
Drain the pasta, and put in oven-proof bowl. Pour over the soya milk and asparagus mixture. Sprinkle over the nutritional yeast (you could use vegan cheese instead). Put under the grill for five minutes, or until brown.
Nutritional information - this comes out at about 550 calories for a standard serving of pasta.