Season meat with pepper. Spray large non-stick skillet with non-stick cooking spray. Add meat; cook for 5 minutes or until cooked through. Remove meat from skillet; cover to keep warm.
Add onions, bell peppers, mushrooms, salad dressing and water to skillet. Bring to a boil. Stir in rice; cover.
Reduce heat to medium-low; simmer for 5 minutes. Remove from heat. Add meat mixture; stir. Let stand, covered, for 5 minutes. Spoon meat mixture evenly onto tortillas and top with sour cream, if desired. Roll up.