1. In a small bowl, stir together lime juice, oil, salsa, cumin and salt. In a large bowl, stir together rice and corn, breaking up any rice clumps.
2. Pour lime-juice mixture over rice mixture and stir well to coat. Add beans, bell pepper, tomatoes and scallions, and toss gently to combine.
3. Just before serving, pit, peel and dice avocado, and stir gently into salad. Sprinkle with cilantro, if desired, and serve.