1. Cut radicchio heads in half lengthwise; cut out and discard cores. Thinly slice radicchio crosswise and transfer to a large bowl. Peel and core pears; cut into 1/2-inch chunks. Add pears and cheese to bowl with radicchio.
2. In a small bowl or glass measure, mix lemon juice, olive oil, and salt to taste. Pour over radicchio mixture and mix gently to coat. Serve at once.