1. Preheat a gas grill to medium. Oil grates; grill peppers, turning once or twice, until charred, 10 to 15 minutes. Transfer to a bowl; cover tightly. Let stand 10 minutes. Remove from bowl; scrape away skin.

2. Brush corn with 1 Tbsp. olive oil; season with salt and pepper. Grill corn, turning, until lightly charred, 7 to 10 minutes. Remove from heat and cool.

3. In a large bowl, whisk vinegar and mustard. Season with salt and pepper and whisk in remaining olive oil. Dice peppers; cut corn kernels from cobs. Mix peppers, corn, scallions and cilantro in bowl with dressing and toss. Season with salt and pepper. Serve at room temperature.