Halve and pit the avocado. Scoop the flesh into the bowl of a food processor. Add the sour cream, 2 teaspoons of the lime juice, ¼ teaspoon of the cumin, and ¼ teaspoon salt. Blend just until smooth. Transfer the crema to a bowl, cover and refrigerate for up to 2 days.
In a large bowl, combine the cabbage, bell pepper, onion, jalapeño, the remaining 2 tablespoons lime juice, 1 ½ tablespoons of the olive oil, cilantro, the remaining ½ teaspoon cumin, and ¼ teaspoon salt. Toss to combine. Cover the slaw and refrigerate until ready to serve.
Spray the broiling pan with nonstick cooking spray. Place the tilapia fillets on the tray and lightly coat both sides with the remaining 2 tablespoons of olive oil. Season with the remaining ¼ teaspoon cumin, salt, and pepper.
Place the broiling pan on the upper level.
Turn on Broil/Grill function. Cook for 10 minutes, or until the fish is just cooked through.
To assemble the tacos, place 2 tortillas on a plate and top each with half a fillet of fish. Stir the cabbage slaw well and top each piece of fish with the slaw and the crema. Repeat to assemble the remaining tacos. Serve immediately with lime wedges.