Preheat your grill or skillet over medium-high heat.
In a bowl, mix the ground beef with salt, pepper, garlic powder, and onion powder.
Divide the beef into 8 equal portions. Flatten each portion into a patty and place a cube of cheese in the center of 4 patties. Top each with another patty and seal the edges.
Grill the burgers for about 5 minutes on each side or until cooked to your liking.
For the mashed potatoes, boil the potatoes in salted water until tender, about 20 minutes. Drain and return to the pot. Add butter, milk, salt, and pepper, and mash until smooth.
For the peas, heat the butter in a skillet over medium heat. Add the peas and cook until heated through, seasoning with salt to taste.
Serve the cheese-stuffed steakburgers with a side of mashed potatoes and peas.