In a bowl soak cranberries in warm water to cover 15 minutes. Drain cranberries well and chop fine. Preheat oven to 350°F. In bowl of a standing electric mixer beat cranberries, oats, and zest into basic dough until just combined well. Form dough into 1-inch balls and roll balls in sugar to coat. Arrange balls 2 inches apart on baking sheets and flatten to 2-inch rounds with bottom of a glass wrapped in wax paper to prevent sticking. Bake cookies in batches in middle of oven until pale golden, about 12 minutes, and cool on racks. Cookies may be stored between layers of wax paper in airtight containers up to 6 weeks frozen.