Sauté first 3 ingredients, 1/4 teaspoon salt, and pepper in a 10-inch ovenproof skillet over medium-high heat 5 to 7 minutes, stirring until beef crumbles and is no longer pink. Remove mixture from skillet, and drain. Wipe skillet clean with paper towels.
Heat oil in skillet over medium-high heat; press hash browns into bottom of skillet and evenly up sides with back of a spoon. Cook 5 minutes. Remove from heat, and spoon beef mixture and cheese spread over hash browns. Stir together milk, eggs, and remaining 1/4 teaspoon salt; pour over cheese spread. Arrange seasoned shredded potatoes around edge of skillet, pressing into meat mixture.
Bake at 350° for 30 minutes or until set. Let stand 10 minutes. Serve with plum tomato slices.