1. Preheat oven to 375°.
2. Heat olive oil in a large skillet over medium-high heat. Add onion; sauté for 3 minutes. Add squash; sauté for 5 minutes. Add apple; cook 6 minutes or until squash and apple are tender. Stir in salt and pepper. Remove from heat, and cool to room temperature. Gently stir in cheese and thyme.
3. Separate dough into 8 pieces. Roll each portion into a 5-inch circle on a lightly floured surface. Combine mustard and 2 teaspoons water in a small bowl. Lightly brush top sides of dough circles with mustard mixture. Spoon about 2 tablespoons squash mixture onto half of each circle, leaving a 1/4-inch border. Fold dough over filling; press edges together with a fork to seal. Brush milk over dough. Place turnovers 1 inch apart on a baking sheet lightly coated with cooking spray. Bake at 375° for 19 minutes or until golden brown. Serve warm.