Peel, seed, and slice the papaya, reserving 1 tablespoon of the seeds for the dressing.
Combine in a large salad bowl the papaya slices, lettuce, radicchio, red onion, and cilantro; toss gently to mix.
To prepare dressing, use a blender of food processor and combine salad oil, sesame oil, lemon juice, vinegar, sugar substitute, and salt. Cover and blend or process until smooth. Add reserved papaya seeds; blend or process until seeds are the consistency of coarsely ground pepper. Pour dressing over salad. Toss lightly to coat.