Heat broiler to high with the rack 6 inches from the flame.
Cut the top quarter off the squash and scoop out the seeds. Cut into thin rings and spread in an even layer on a rimmed baking sheet. Combine the oil, syrup, and Sriracha and brush over the squash. Season with 1 teaspoon salt and ½ teaspoon pepper.
Broil until toasted and warmed through, 10 minutes. Sprinkle with the cilantro and serve warm.