Bring a large pot of water to a boil for the pasta.
In a medium skillet, cook the nuts over medium heat, stirring often, until toasted, about 4 minutes. (Or toast in a 400° oven until fragrant, about 4 minutes.) Let cool. Place in a food processor with the herbs, cheese, lemon juice and garlic; season with salt and pepper and pulse until finely chopped. With the machine running, stream in the EVOO to form a pesto. Transfer the pesto to a serving bowl.
In a large skillet, heat the olive oil, one turn of the pan, over medium-high. Add the sausage; cook, stirring often and breaking up with a spoon, until browned, 5 to 6 minutes. Add the peas and shallots; cook, stirring constantly, until the shallots soften, about a minute. Add the stock and reduce the heat to medium-low; season. Let the sauce simmer while you cook the pasta.
Salt the boiling water, add the pasta and cook until a bit shy of al dente. Reserve half a mug of starchy cooking water; drain. Add the sausage mixture, pasta and half the starchy water to the pesto. Toss, adding more starchy water if too dry; season. Serve in shallow bowls.