Heat oil in a nonstick skillet, add one tortilla. Layer with half the cheddar cheese and all of the meat and mushrooms and half of the Monterey Jack cheese. Top with the second tortilla. Cover and heat until cheese melts and bottom of tortilla is crisp and golden brown. Turn over, sprinkle remaining cheeses on top. Cook until cheese is melted. Cut into wedges, serve with sour cream and salsa.