Preheat oven to 350F. Brush 13 x 9 x 2-inch glass baking dish with oil. Heat 2 tablespoons oil in heavy large skillet over high heat. Add mushrooms and saute until golden, about 10 minutes.

Pour enchilada sauce into shallow bowl. Dip 1 tortilla into sauce. Place tortilla on piece of wax paper. Spread 1 tablespoon sour cream across center of tortilla. Mound 1/4 cup chicken over. Top with 3 tablespoons mushrooms, then 1 tablespoon chilies and 1/4 cup cheddar cheese. Fold bottom half of tortilla over filling and roll up to enclose completely. Place enchilada in prepared dish seam side down. Repeat dipping and filling with remaining tortillas, sour cream, chicken, mushrooms, chilies and cheddar cheese. Spoon remaining enchilada sauce evenly over. (Can be prepared 1 hour ahead. Cover enchiladas and let stand at room temperature.)

Bake until enchiladas are heated through, about 30 minutes.