1. Make dip: Puree all ingredients in a food processor until smooth, with red and green flecks still visible. Cover and chill.
2. Make sweet potatoes: Bring a large pot of salted water to a boil; add potato wedges. Cook for 5 minutes. Drain on a paper towel-lined tray; pat dry. Let cool. Preheat grill to medium. Oil grates.
3. Toss potato wedges with oil; sprinkle with garlic salt. Grill potatoes, turning often, until just tender and slightly charred, 8 to 10 minutes. Just before serving, taste dip; add additional salt and pepper, if desired. Serve potato wedges with dip on the side.