Preheat oven to 375°.
Cook rice according to package directions, omitting salt and fat.
Heat oil in a large nonstick skillet coated with cooking spray over medium-high heat. Add mushrooms and onion; sauté 5 minutes or until tender. Combine enchilada sauce, tomato juice, and mushroom mixture. Spoon 1/4 cup mushroom mixture over bottom of an 11 x 7-inch baking dish coated with cooking spray.
Combine rice, chicken, and next 6 ingredients in a large bowl. Spoon about 1/2 cup chicken mixture in center of 1 tortilla; roll tightly and place, seam side down, in baking dish. Repeat procedure with remaining tortillas and chicken mixture.
Spoon remaining mushroom mixture over top of enchiladas. Cover and bake at 375° for 25 minutes. Uncover; sprinkle with Cheddar cheese. Bake an additional 4 minutes or until cheese melts. Let stand 5 minutes. Top each enchilada with 1 tablespoon sour cream.