Preheat oven to 350°F. Mix soup and milk, then add pepper and green beans. Stir in cup French fried onions. Pour into a 1 1/2 quart casserole. Bake for 30 minutes or until hot. Remove from oven and stir casserole. Top with prepared mashed potatoes. Adjust oven to broil. Toast potatoes under broiler until lightly brown, about 2 minutes. Top with remaining French-fried onions and serve.