Heat oven to 375°F. Spray 2 1/2-quart round or oval baking dish with cooking spray.
In 12-inch nonstick skillet, cook beef and onion over medium-high heat 6 to 8 minutes, stirring occasionally, until thoroughly cooked; drain.
Reduce heat to medium. Add frozen mixed vegetables, tomato paste, Italian seasoning, salt and pepper. Cook 4 to 5 minutes, stirring frequently, until thoroughly heated.
Meanwhile, in small bowl, mix broth and flour with whisk until well blended. Add broth mixture to beef mixture. Cook 2 to 3 minutes, stirring occasionally, until thickened. Spoon beef mixture into baking dish.
Meanwhile, cook mashed potatoes as directed on package. Spread evenly over beef mixture.
Bake 20 to 25 minutes or until heated through.