Place oven rack 6 in. from heat; preheat broiler to HIGH. Line a rimmed baking pan with foil; set aside.

Cut off a ½-in. slice from top and bottom of each grapefruit. Using a sharp knife, remove the entire peel and outer white membranes from each grapefruit by cutting from top to bottom. Cut each grapefruit crosswise in half; remove seeds with point of paring knife.

Place grapefruit halves, cut sides up, in prepared baking pan. Sprinkle with sugar. Broil for 8 to 10 minutes or until sugar is caramelized and dark brown. Cool slightly. Reserve grapefruit juices in pan for serving.

Meanwhile, combine almonds, lime zest, Aleppo pepper and salt in a small bowl; set aside.

To serve, divide yogurt among 4 serving plates. Arrange 2 grapefruit halves on each plate. Sprinkle with almond mixture. Drizzle with grapefruit juices, if desired.