Spray a medium skillet with nonstick spray. Add onions and garlic. Cook over low heat, stirring often, until translucent. Add spinach to the pan, toss to combine and let cook until wilted, about 2 minutes. Remove from heat and let cool slightly. Season turkey slices with freshly ground pepper. Add one quarter of spinach mixture and roll tightly to form roulades.
Place roulades in a large skillet. Add turkey stock and warm over medium heat until just heated through and moist, about 5 minutes. Place roulades on a plate with a serving of mashed sweet potatoes. Garnish with fresh cranberries. Serves 4.