Italian Beef with Mashed Potatoes

2 teaspoons vegetable oil
1 lb boneless beef sirloin, trimmed of fat, cut into thin bite-size strips
1 can (6 oz) Italian-style tomato paste
1 cup water
1 packet (from 1.1-oz box) very-low-sodium beef-flavor bouillon
1/2 teaspoon crushed red pepper flakes
1 bag (1 lb) frozen stir-fry bell peppers and onions, thawed, drained
1 1/3 cups Betty Crocker® Potato Buds® mashed potatoes (dry)
1 1/3 cups water
1/3 cup fat-free (skim) milk
1 tablespoon butter or margarine
1/2 teaspoon salt

In 12-inch skillet, heat oil over medium-high heat. Add beef; cook and stir about 5 minutes or until browned. In medium bowl, mix tomato paste, 1 cup water, the beef bouillon and red pepper flakes. Add tomato mixture and stir-fry vegetables to skillet. Cook about 3 minutes, stirring occasionally, until mixture boils. Cook 3 to 5 minutes longer or until vegetables are tender. Meanwhile, make mashed potatoes as directed on package, using 1 1/3 cups water, the milk, butter and salt. Serve beef mixture over mashed potatoes.