Trim fat from pork; cut pork into 2-inch pieces. Combine pork, water, and next 5 ingredients in a saucepan; bring to a boil. Cover, reduce heat, and simmer 30 minutes. Uncover; cook over medium-low heat 1 hour or until liquid evaporates. Remove from heat; shred meat with 2 forks. Stir in tomato sauce, chiles, cheese, and green onions.
Wrap tortillas in aluminum foil; heat at 350° for 15 minutes. Working with 1 tortilla at a time, coat both sides of tortilla with cooking spray. Spoon about 1/3 cup meat mixture just below center of tortilla. Fold over left and right sides of tortilla to partially enclose filling. Fold remaining edges to form a rectangle, and secure with a wooden pick. Repeat procedure with remaining tortillas and meat mixture. Place filled tortillas on an ungreased baking sheet. Bake at 425° for 20 minutes or until crisp. Remove wooden picks. Place 1 cup lettuce on each of 12 plates; top with chimichangas. Combine sour cream and hot sauce. Top each chimichanga with sour cream mixture and salsa.