Adjust oven rack to the highest position; heat broiler.
Cook the rice according to the package directions.
Meanwhile, cut the poblanos in half lengthwise. Scoop out and discard the seeds. Place the poblanos skin-side up on a foil-lined baking sheet. Broil until the skin is charred black, 2 to 3 minutes. Remove from oven and let cool.
In a large bowl, combine the corn, beans, cooked rice, oil, 1 1/4 teaspoons salt, and 1/4 teaspoon pepper. Using your fingers or a paring knife, peel the poblanos and discard the skins. Divide the poblano halves among individual plates. Spoon the rice mixture over the tops and sprinkle with the cheese. Serve at room temperature.
Tip: Poblanos (mild green peppers with a sturdy flesh that's perfect for stuffing) are available in many supermarkets. But if you can't find them, try small green bell peppers instead.