Cook peas on the stove or in a microwave according to package directions, then drain well.
With food processor running, drop in garlic and finely chop. Turn off motor and add peas, nuts, cheese, 1/2 teaspoon salt, and 1/2 teaspoon pepper, then process until finely chopped. With motor running, add oil, blending until incorporated.
Meanwhile, cook pasta in a large pasta pot of boiling salted water (3 tablespoons salt for 6 quarts water) until al dente. Reserve 1 cup pasta-cooking water, then drain pasta in a colander.
Toss pasta with pea pesto and thin as desired with reserved cooking water. Season with freshly ground pepper.
