Place first 4 ingredients in a saucepan; bring to a boil, reduce heat, and cook 4 minutes.
Add green beans; cook 5 minutes. Coat a nonstick skillet with cooking spray; add oil.
Place over medium-high heat until hot.
Add onion; saute 5 minutes.
Sprinkle flour over onion; stir.
Add broth mixture to onion; stir.
Add Worcestershire sauce, tomato paste, and pepper; cook over medium heat until thickened, stirring frequently.
Add Savory Pot Roast; cook 2 minutes.
Cook potato in boiling water to cover 10 minutes or until tender.
Drain; mash.
Add milk; beat at medium speed of an electric mixer until smooth. Stir in sour cream, salt, and 1 teaspoon chives. Spoon beef mixture into 2 (1 1/2-cup) casseroles coated with cooking spray.
Spread potato topping over beef mixture; crisscross with tines of fork.
Bake, uncovered, at 350 for 20 minutes.
Sprinkle with cheese and remaining chives; bake 5 minutes.