Bring a large pot of water to a boil over high heat. Add salt and stir in the penne. Reduce to medium-high and cook penne, uncovered, until al dente, 6-7 minutes.
Meanwhile, place walnuts on a rimmed baking sheet and bake in preheated 350-degree o ven until lightly toasted, 4-5 minutes.
Place pesto and blue c heese in a large serving bowl and using a fork, mash the blue cheese into the pesto.
Rinse asparagus spears and snap off and discard their tough ends. Break spears into 1 1/2-inch long pieces.
During the last 3 minutes of the penne cooking time, add asparagus to pot and cook until bright green and crisp-tender. Drain penne and asparagus well in colander. Add to the bowl with the pesto and stir to coat them well. Top with toasted walnuts and serve at once.