Bring a large pot of salted water to a boil. Add the pasta and cook as the label directs, adding the snap peas during the last 2 minutes of cooking. Reserve 1 cup of the cooking water, then drain.
Meanwhile, heat 2 tablespoons butter in a large skillet over medium-high heat. Add the shallot and cook, stirring, until slightly softened, about 2 minutes. Add the salmon; season with 3/4 teaspoon salt and a few grinds of pepper. Cook, turning once, until the salmon is just cooked through, about 3 minutes. Transfer to a plate.
Add the pasta and snap peas to the skillet along with 1/2 cup of the reserved pasta cooking water, the remaining 2 tablespoons butter, the herbs and lemon juice. Cook, tossing and adding more of the reserved cooking water if necessary, until the pasta is coated, about 1 more minute. Season with salt and pepper. Top with the salmon.
Photograph by Antonis Achilleos
Courtesy of Food Network Magazine