1. Heat a large nonstick skillet over medium-high heat. Coat pan with cooking spray. Add onion; sauté 2 minutes. Add jalapeño; sauté 2 minutes. Sprinkle sugar over onion mixture; sauté 1 minute. Remove onion mixture from pan.
2. Return pan to heat; recoat with cooking spray. Add mushrooms and garlic to pan; sauté 1 minute. Add Madeira to pan; cover, reduce heat, and simmer 2 minutes. Uncover; cook 2 minutes or until liquid evaporates, stirring frequently. Stir in onion mixture and chicken; cook 3 minutes or until thoroughly heated.
3. Warm tortillas according to package instructions. Spoon about 1/3 cup chicken mixture onto each tortilla. Top each tortilla with 2 tablespoons cheese; fold in half. Serve with sour cream.