COMBINE sugar, cornstarch and cinnamon in medium, heavy-duty saucepan; gradually stir in evaporated milk, water and egg yolk. Bring to a boil over medium heat, stirring constantly, until mixture is slightly thickened. Remove from heat; stir in vanilla extract. Cover; keep warm.
COMBINE water, apricots, apples, nuts, sugar and cinnamon in medium saucepan. Bring to a boil. Reduce heat to medium; cover. Cook, stirring occasionally, for 10 to 15 minutes or until excess moisture is absorbed. Cool for 15 minutes.
PLACE ¼ cup filling in center of each tortilla. Fold into burritos; secure ends with wooden picks. Add vegetable oil to 1-inch depth in medium skillet; heat over high heat for 3 to 4 minutes. Place 2 or 3 chimichangas at a time in oil; fry, turning frequently with tongs, for 1 to 2 minutes or until golden brown. Place on paper towels to soak. Remove wooden picks. Serve with Cinnamon Custard Sauce.