Cook spaghetti according to package directions until al dente. Meanwhile, in a food processor, combine peas, 1/4 cup pine nuts, Grana Padano cheese, lemon juice, garlic clove, salt, and pepper until chunky. With processor running, add olive oil in a slow stream until smooth. Reserve. Drain spaghetti, but do not rinse. Toss pasta with reserved pesto. Divide pasta among 4 bowls and top each with 2 tablespoons part-skim ricotta, some torn fresh mint leaves, and 1 1/4 teaspoons toasted pine nuts.