In a medium bowl combine avocado, lime peel and juice; toss to coat. Add crabmeat, tomato, cilantro, dip and pepper; toss lightly to mix. Cover and refrigerate 15 minutes.
Meanwhile, coat grill rack with nonstick cooking spray. Preheat grill to medium-high (350F to 400F). Place polenta slices on grill; grill 2 to 3 minutes per side or until lightly charred and heated through.
Spoon crab mixture onto polenta slices. Sprinkle with additional cilantro and serve.