Preheat the oven to 425°F (use convection if available). Line a sheet pan with heavy-duty foil if desired and lightly spray or oil the pan.
On the prepared sheet pan, spread the halved or quartered potatoes and diced bell pepper in a single layer.
Drizzle the vegetables with 3 tablespoons olive oil, then sprinkle with 1 teaspoon kosher salt, 1/2 teaspoon black pepper, and 1 to 1 1/2 teaspoons Madras curry powder. Toss with your hands or tongs to coat evenly.
Bake the vegetables for about 15 minutes, or until the potatoes are at least halfway tender when pierced with a fork.
Remove the pan from the oven and evenly distribute the diced chicken breast among the vegetables.
Drizzle the remaining 3 tablespoons olive oil over the chicken and vegetables, then sprinkle with the remaining 1 teaspoon kosher salt (adjust to taste), remaining 1/2 teaspoon black pepper, and 1 to 1 1/2 teaspoons Madras curry powder. Toss gently to combine so the chicken is coated.
Return the sheet pan to the oven and bake for about 15 minutes more, or until the chicken is cooked through and the potatoes are tender.
Scatter the frozen peas over the pan (no need to thaw) and bake 1 to 2 minutes more, until the peas are just warmed through. Serve immediately.