1Heat oven to 450°F. Divide pizza dough into 8 pieces. Roll out each into 8-inch round disk.
2To make filling, in 10-inch skillet, heat oil over medium to medium-high heat. Add onion, bell pepper, zucchini and mushrooms; cook 5 to 7 minutes or until vegetables begin to soften. Add spinach; continue to cook about 2 minutes or until spinach wilts. Stir in garlic; cook 1 minute longer. Remove from heat; set aside to cool slightly.
3To make each calzone, spread 2 tablespoons pesto on dough round. Top with filling. Sprinkle with 1/4 cup Gouda cheese. (Resist the temptation to overfill the dough.) Fold dough over; press edge and twist to seal. Place on ungreased cookie sheet.
4Bake 15 to 20 minutes or until golden brown. Cut calzones in half to serve.