Preheat your oven to 375°F (190°C) and line a baking sheet with parchment paper to prevent sticking and make cleanup easier.
In a medium bowl, combine the diced apples, sugar, flour, cinnamon, nutmeg, and lemon juice. Stir until the apples are evenly coated with the sugar-spice mixture. The flour will help thicken any juices that release during baking.
Unroll the crescent dough and separate into triangles along the perforated lines. If using crescent roll sheets, cut into 8 equal triangles per sheet.
Place about 1-2 tablespoons of the apple mixture on the wider end of each triangle, being careful not to overfill (which could cause leakage during baking).
Carefully roll up each triangle, starting from the wide end with the filling and rolling toward the pointed end. Gently curve the ends inward to form a crescent shape.
Place the turnovers on the prepared baking sheet, spacing them about 2 inches apart to allow room for expansion.
Brush each turnover with the beaten egg using a pastry brush, then sprinkle with coarse sugar for a beautiful, sparkly finish and extra crunch.
Bake for 12-15 minutes or until golden brown. Watch carefully in the last few minutes to prevent over-browning.
Allow to cool for 5-10 minutes before serving to let the filling set slightly and avoid burning your mouth on the hot filling.
If desired, drizzle with a simple powdered sugar glaze for extra sweetness and visual appeal.