Cook the penne pasta in a large pot of boiling, salted water. Cook until almost tender but still firm to the bite. Drain and chill the pasta in the refrigerator.

While the pasta is cooking, make the dressing. Combine the mayonnaise, sour cream, dill, lemon juice and poppy seeds in a medium bowl. Refrigerate.

Rinse the asparagus and trim off the tough ends. Cut into 1-inch pieces. Cover with water and cook in the microwave until crisp tender. Drain in a colander, but reserve ? cup of the cooking liquid to add to the dressing. Chilled the drained asparagus.

Dice the lox and stir into the dressing. Add the sliced green onions and reserved asparagus cooking liquid. Gently stir the dressing and chilled pasta together. Fold in the asparagus and serve chilled.