Heat oven to 450°F. Place bread slices on ungreased cookie sheet. Bake 4 to 5 minutes or until toasted.
Meanwhile, cook beef roast in microwave as directed on package. Cool slightly. Shred 1 cup beef with 2 forks. (Reserve remaining beef roast and au jus for later use.)
In 12-inch nonstick skillet, heat oil over medium-high heat. Cook peppers, salt and pepper in oil 5 minutes, stirring frequently, until peppers are tender.
Set oven control to broil. Top toasted bread slices evenly with shredded beef, pepper mixture and cheese. Broil with tops about 6 inches from heat 1 to 2 minutes or until cheese is melted and light golden brown.