Set pot to saute, add ground beef, onion, bell peppers and garlic salt. Brown until no longer pink. Turn pot off. Drain grease out of pot. Add potatoes into the beef mixture and toss.
On the stovetop in a pan (or remove meat, drain, and make roux on saute in IP). Melt the butter, add flour and whisk until incorporated. Add milk and stir until it bubbles and thickens. Add cheese and stir until melted.
Combine meat mixture and sauce, toss together so it is all well incorporated.
Empty pressure cooker pot and rinse out. Pour 2 cups of water into the bottom with a trivet inside.
Spoon potato ground beef mixture into a ceramic baking dish that will fit inside your IP.
Set dish on top of trivet and close lid. Cook on high for 15 minutes with a quick release when done.
Lift out and serve. Sauce will continue to thicken as it sits and cools.