Set the Instant Pot to sauté mode and add the ground beef and onion. Season with garlic powder, black pepper, and salt. Sauté until beef is browned.
Turn off the Instant Pot and add the Worcestershire sauce and tomato paste. Stir to combine.
Add the beef broth and water. Use a wooden spoon to scrape the bottom of the pan to remove stuck-on food.
Add the macaroni and stir to combine. Make sure all the noodles are covered with liquid, then place the lid on the Instant pot and seal the vent.
Set the Instant Pot to pressure cook for 5 minutes. When the cook time is up, do a quick release and remove the lid.
Add both cheeses and stir until the cheese is melted and well combined.
Serve topped with green onion, if desired.