Preheat oven to 400°F.
In a large bowl, toss potato halves and diced red bell peppers with 1 tbsp olive oil, salt, and pepper.
Spread on a parchment lined baking sheet in a single layer. Place corn on a separate baking sheet.
Place potatoes and peppers on middle rack, and the corn on the bottom rack. Roast 30 minutes. Remove corn from oven and continue roasting potatoes and peppers 30 more minutes, or until potatoes are tender. Meanwhile, remove husks from corn and slice off the kernels.
In a small mixing bowl, whisk together olive oil, lemon juice, mustard, dill, and parsley. Add salt and pepper to taste.
Place roasted potatoes, red peppers, and corn kernels in a large bowl. Add diced red onion and scallion. Drizzle dressing over vegetables. Toss to combine.
Salad can be enjoyed warm or room temperature. Store leftovers covered in refrigerator.