Brown ground beef with onion powder, garlic powder, salt, and pepper in a skillet over medium-high heat for 6-8 minutes, breaking apart until cooked through.
Drain excess grease and transfer beef to slow cooker.
Whisk together Worcestershire sauce, tomato paste, beef broth, brown gravy powder, cream of mushroom soup, and cream of chicken soup until smooth.
Pour sauce over beef in slow cooker and stir to combine.
Cover and cook on low for 6 hours total.
After 5 hours, stir in frozen mixed vegetables.
Prepare instant mashed potatoes according to package directions and season with salt, pepper, and butter.
Spread mashed potatoes evenly over meat mixture, cover, and cook for final hour.
Let rest 10 minutes before serving.