1. Cover dried beans with 2 inches of cold water. Refrigerate overnight. (Or combine beans with water to cover by 2 inches in a 3-quart saucepan. Bring to a boil; boil 2 minutes. Remove from heat. Cover and let stand 1 hour. Drain beans in colander. Return beans to saucepan and add cold water to cover by 2 inches; bring to a boil. Reduce heat and simmer 50 minutes, until beans are tender.
2. Meanwhile, for corn salsa, heat a large nonstick skillet over high heat 2 minutes. Add 1 teaspoon of the oil and the corn. Cook 3 minutes, until edges of corn brown. Stir in tomatoes-and-green-chilies mixture; cook 5 minutes, until mixture thickens slightly. Transfer to a bowl; stir in orange juice and cilantro. Set aside.
3. Wipe out skillet with a paper towel. Heat skillet over high heat 1 minute; add remaining 1 teaspoon oil, the mushrooms and cumin. Cook 2 to 4 minutes, until mushrooms soften. Add onion and salt; cook 5 minutes more, until onion is softened. Add beans and 1/3 cup water (or canned beans and 1/4 cup water) to skillet.
4. For each quesadilla, sprinkle 1 tablespoon cheese on 1 tortilla; spoon 3/4 cup bean mixture over top. Sprinkle beans with 1 more tablespoon cheese; top with another tortilla.
5. Heat and oil a grill pan over medium heat 2 to 3 minutes. Grill quesadillas in batches 2 to 3 minutes per side, until dark grill marks are formed and cheese has melted. Serve with corn salsa. Makes 4 servings.