Spring Vegetable Penne with Lemon-Cream Sauce

If you can find it, use peeled fresh English peas instead of frozen ones.
Preheat a large skillet over medium-high heat. Add the butter; stir to coat. Add the onion and mushrooms; simmer for 5 minutes or until tender. Add thyme and garlic; simmer for 1 minute. Sprinkle the mushroom mixture evenly with flour; cook for 30 seconds, stirring constantly. Add the stock and stir in half; cook for 2 minutes or until slightly thickened. Add the peas, 2 tablespoons of cheese, zest, and the next 3 ingredients (season with pepper); cook for 1 minute or until the peas are thoroughly warmed through.Prepare the pasta according to the instructions on the package, without adding salt or fat. During the last 3 minutes of cooking, add the asparagus to the pan; drain. Add the pasta mixture to the mushroom mixture; stir gently to coat. Sprinkle with the remaining 1 tablespoon of cheese.