1. In a medium bowl, stir together the black beans, corn, squash, green onions, cilantro, chili powder, garlic, cumin, coriander, and pepper. Stir in 1/2 cup each of the Monterey jack and cheddar cheeses.
2. Coat a 6-qt. slow cooker with cooking spray. Spread 1/2 cup of the salsa over the bottom of the cooker. Spoon 1/4 cup of the black bean filling into one tortilla, roll it up, and arrange it, seam side down, in the slow cooker. Fill and roll 5 more tortillas and arrange them in a single layer in the bottom of the slow cooker. Spread 1/2 cup of the salsa over the tortillas, and sprinkle with 1/4 cup each of the Monterey jack and cheddar cheeses.
3. Fill and roll the remaining tortillas, and arrange them on top of the tortillas in the slow cooker to form a second layer. Spoon any leftover filling along the sides. Spread the remaining 1 cup of salsa over top. Sprinkle with remaining cheese. Cover and cook on high for 2 to 2 1/2 hours, or until the vegetables and tortillas are tender and center reaches 165 degrees F.
4. Turn off the slow cooker, pull out the insert (if it comes out), and remove the lid. Let stand 5 minutes. Top with additional green onions, cilantro, and radishes.