1Heat oven to 400°F. Spray large cookie sheet with cooking spray. Remove pie crust from pouch; on lightly floured surface, roll crust into 13-inch round. Carefully transfer to cookie sheet.
2In 12-inch nonstick skillet, melt butter over medium heat. Cook onion in butter 5 minutes, stirring frequently, until tender. Add garlic and thyme; cook 1 minute or until fragrant. Add Swiss chard; cook 3 minutes or until just wilted. Stir in vinegar; cook 1 minute longer. Remove from heat.
3Spread goat cheese on dough round to within 11/2 inches of edge. Top with chard mixture, Parmesan cheese and walnuts. Fold edges of dough over filling, making pleats so pastry lays flat. Bake 40 to 45 minutes or until golden brown. Cool 5 minutes. Cut into wedges.