For the slaw: In a large bowl, lightly toss the shredded cabbage, removing any thick pieces. Repeat with the radicchio, then add to the cabbage. Add the jicama, carrots, red bell peppers, green onions, cilantro and pineapple, tossing after each addition.
For the cumin dressing: Combine the mayonnaise, cumin, 1/2 teaspoon salt, 1/2 teaspoon pepper and agave in a measuring cup. Whisk in the grapefruit juice, orange juice and vinegar and blend well.
Pour the vinaigrette over the slaw mix and blend well. Refrigerate for 20 minutes. Stir and serve.