Place a baking sheet on the bottom rack of the oven to catch any spillovers from skillet then preheat oven to 400 degrees.
Place a large, 12" oven-safe skillet over medium-high heat then add ground beef and shallots. Season with homemade seasoned salt and pepper, then brown the beef. Add garlic and dried herbs then saute for 1 minute or until garlic is very fragrant. Add tomato paste and worcestershire sauce then stir to combine. Sprinkle in flour then stir to combine and cook for 1 minute.
Gradually add splashes of beef broth while stirring to avoid lumps then simmer, stirring often, until mixture has thickened, 3-4 minutes. Taste then add more seasoned salt and/or pepper if necessary. Remove skillet from heat then stir in frozen vegetables.
Spoon mashed potatoes on top of meat and vegetables then spread into an even layer. Combine butter and garlic powder in a small dish then use a pastry brush or spoon to brush or drizzle the garlic butter on top. Run a fork around the mashed potatoes like recipe photos.
Bake for 15-20 minutes or until dish is bubbly. Place under broiler set to high to get the top golden brown. Let cool for 5 minutes before serving.
Notes
I recommend my homemade Healthy Mashed Potatoes for this recipe. If you want to use store-bought, Bob Evans and Simply Potatoes brand prepared mashed potatoes are great too. Check packaging to ensure they are gluten free before buying.
Homemade All Potato Mashed Potato recipe (makes 4-1/2ish cups): Peel then chop 2lbs Yukon Gold or Russet potatoes and add to a large pot of cold water. Bring to a boil then cook until potatoes are tender, 8-12 minutes, and then drain. Add 1/3 cup (5 Tablespoons) butter or vegan butter, 1/2 cup milk (any kind), salt, and pepper to the pot then add potatoes and mash until smooth. Alternatively you could rice the potatoes into the pot with the milk and butter then stir to combine. Measure out 4 cups then use remaining potatoes for something else. Mashed potatoes can be made several days ahead of time.