In a large skillet, cook beef and onion over medium heat until meat is no longer pink; drain. Stir in taco seasoning and water. Bring to a boil. Reduce heat; simmer, uncovered, for 5 minutes, stirring occasionally. Remove from the heat; cool slightly.
In a large bowl, combine the cheese, sour cream and chiles. Stir in beef mixture. Place an egg roll wrapper on work surface with a point facing you. Place ⅓ cup filling in center. Fold bottom third of wrapper over filling; fold in sides.
Brush top point with egg white; roll up to seal. Repeat with remaining wrappers and filling. (Keep remaining egg roll wrappers covered with waxed paper to avoid drying out.)
In a deep cast-iron or electric skillet, heat 1 in. oil to 375°. Fry chimichangas on each side or until golden brown, 1-½ minutes. Drain on paper towels. Serve warm with salsa and sour cream.
