In a medium bowl, mash half the beans. Add the spinach, corn, cumin, 1 cup of the Cheddar, the remaining beans, ½ teaspoon salt, and ¼ teaspoon pepper and mix to combine.
Spread 1 jar of the salsa in the bottom of a 4- to 6-quart slow cooker. Dividing evenly, roll up the bean mixture in the tortillas (about ½ cup each) and place the rolls seam-side down in a single layer in the slow cooker. Top with the remaining salsa and Cheddar.
Cover and cook until heated through, on low for 2½ to 3 hours.
Before serving, toss the lettuce, radishes, tomatoes, and cucumber in a large bowl with the lime juice, oil, and ½ teaspoon each salt and pepper. Serve with the enchiladas and sprinkle with the scallions.