In a heavy skillet cook onion and mushrooms in oil over moderate heat, stirring, until golden. Add spinach and garlic and cook, stirring, until spinach is wilted, about 30 seconds. Stir in water, beans, lemon juice, scallions, pepper Jack, salt, to taste, and cook stirring, until cheese is melted.
In a small saucepan, heat enchilada sauce.
Heat a dry skillet (large enough to hold 1 tortilla) over moderately high heat until hot. In skillet heat tortillas, 1 at a time, turning frequently, 30 seconds, or until softened, and transfer to a work surface. Divide filling between tortillas and roll up burritos.
Spoon sauce over burritos and serve with sour cream.
Recipe courtesy of Gourmet magazine