Step 1

Place beans in a bowl; cover with 2 inches of water. Refrigerate, covered, overnight; drain and rinse. Cover with water in a saucepan. Bring to a boil; cook 10 minutes. Remove from heat; drain and rinse.

Step 2

Place beans, oil, leeks, garlic, pepper flakes, squash, sage, and rind in a 5-to-6-quart slow cooker. Add 8 cups water. Cover and cook on low 6 hours. Remove and discard sage and rind; stir in lemon juice and spinach. Season with salt and pepper. Serve, drizzled with oil and topped with shredded cheese and pepper flakes.