Preheat the oven to 350ºF. Spray a 2-quart baking dish with cooking spray.
In a mixing bowl, combine the peppers, corn, onion, flour or starch, dry mustard, salt, and pepper. In another mixing bowl, whisk together the eggs and milk. Add the eggs and milk to the corn mixture and mix well. Pour into the prepared baking dish and bake for 45 minutes or until set.