1. Place potatoes in a large pot and cover with at least 2 inches of cold water. Bring to a boil over high heat and season generously with salt. Reduce heat and simmer until potatoes are tender and easily pierced with a knife, about 12 minutes. Transfer with a slotted spoon to a cutting board or plate; let cool. Add peas to simmering water and cook 1 minute. Drain and transfer to a bowl filled with ice water to stop cooking. Drain.

2. Whisk together simmer sauce and yogurt in a large bowl until thoroughly combined. Halve potatoes and add to yogurt mixture along with peas, stirring to combine. Refrigerate until chilled, at least 1 hour. Stir in herbs before serving.