Your guests will polish off these spicy meatballs in no time, so you might want to make a double batch!
In food processor, pulse first 4 ingredients and 2 tsp. salt to chop. With machine running, stream in 2/3 cup oil to make piri piri sauce. In bowl, mix chicken, breadcrumbs, onion, and egg with 2 tbsp. sauce; form into 1-inch balls. In skillet, heat 1/2 inch of oil over medium-high. In batches, fry meatballs, turning once, until browned and cooked through, about 8 minutes. Transfer meatballs to bowl. Toss with 2 tbsp. sauce. Serve on platter with toothpicks and remaining sauce for dipping.