Preheat oven to 375 degrees F. Cook lasagna noodles according to package directions just until tender. Drain noodles; rinse with cold water. Drain well; set aside.
In a small bowl, stir together pesto and lemon peel; set aside. In a medium bowl, stir together egg, ricotta cheese, 1 cup of the shredded Italian blend cheese, the salt, and pepper; set aside.
To assemble pie, lightly coat a 9-inch springform pan with nonstick cooking spray.* Line bottom of pan with parchment paper or foil. Lightly coat parchment paper or foil with cooking spray. Arrange four of the cooked noodles in the bottom of the pan, trimming and overlapping as necessary to cover bottom of pan with one layer of noodles. Top with spinach. Sprinkle with walnuts. Spoon half of the ricotta cheese mixture over walnuts, spreading evenly. Spoon one-third of the pesto mixture over ricotta layer, spreading evenly. Top with another layer of noodles, trimming to fit. Top with mushrooms. Spread remaining ricotta cheese mixture over mushrooms. Spread half of the remaining pesto mixture over ricotta layer. Top with another layer of noodles and the remaining pesto mixture. Slice, quarter, or halve tomatoes and place on top of layers.
Place springform pan in a foil-lined shallow baking pan. Bake, covered, for 45 minutes. Uncover and bake about 15 minutes more or until hot in the center. Sprinkle with the remaining 1/2 cup Italian blend cheese. Cover and let stand for 20 minutes. Carefully remove side of springform pan. Using wide metal spatulas, carefully transfer lasagna to a serving platter. If desired, garnish with parsley leaves. To serve, cut lasagna into wedges.