Set the electric pressure cooker to “saute” until “hot.” Add the ground beef, crumbling the beef as it cooks until brown. Drain well.
Pour the water into the electric pressure cooker while still on the saute mode and scrape the bottom with a wooden spoon to help remove and cooked on pieces. Cancel the “saute” mode.
Return the ground beef and onion mixture to the electric pressure cooker.
Place the macaroni, tomatoes, and seasonings into the electric pressure cooker, stirring to distribute the seasonings evenly.
Cover the electric pressure cooker and set the valve to “sealing.”
Program the pressure cooker using the “manual” or “pressure cook” function for 4 minutes. When the cooking cycle is completed, perform a quick release of the pressure. Carefully remove the lid.
Stir in the milk and 4 cups of cheddar cheese. Stir until the cheese is melted. Re-cover and allow to “keep warm” until the liquid is absorbed.
Cover with the remaining cheese and serve.