Add water to a large saucepan to a depth of 1 inch; set a large vegetable steamer in the pan. Add eggs to the steamer. Bring the water to a boil over medium-high heat. Steam eggs, covered, 16 minutes. Remove from heat. Place the eggs in a large ice water-filled bowl for 3 minutes.
While the eggs steam, combine 1/4 cup water, vinegar, and sugar in a medium microwave-safe bowl; microwave at high for 2 minutes or until boiling. Stir in the onion. Let stand at room temperature for 15 minutes. Drain.
Combine yogurt, mayonnaise, mustard, Sriracha, pepper, and salt in a medium bowl, stirring well to combine.
Peel eggs; discard shells. Slice eggs in half lengthwise. Add yolks to the yogurt mixture. Mash with a fork until very smooth. Stir in 2 tablespoons red onion. Spoon the mixture into the egg white halves (about 1 tablespoon in each half). Garnish with remaining red onion and chives.