Cover top of insert with large kitchen towel. Place slow-cooker lid on top of towel. (This will prevent condensation from dripping onto biscuits during cooking.) Cook on Low heat setting 2 hours to 2 hours 30 minutes. Insert paring knife into center of casserole to test that biscuits are fully baked; outer edge will be deep golden brown. Sprinkle with green onion greens. Serve warm.