Cut the boneless, beef chuck into 4 equal sized pieces. Season with salt, pepper, garlic powder, onion powder, and Italian seasoning.
Turn on pressure cooker and push the Saute button. When the liner is hot, add the olive oil and swirl around the bottom to evenly coat. Sear the meat on all sides until browned
Once browned, remove from pressure cooker and place on a plate. Press the Cancel button and pour the beef stock and fish sauce into the liner. Use a wooden spoon to scrape all of the cooked bits off the bottom.
Place the trivet in the liner, then add the browned meat and onion slices.
Place the lid on your Instant Pot and twist to seal. Check to make sure the valve is in the Sealing position, push the Meat or Manual button and adjust the time to 60 minutes
While the meat is cooking, slice the bell peppers and toss them with salt, pepper, and garlic powder. Saute the pepper slices in a skillet with olive oil until softened and lighter in color. Set aside and keep warm.
When the pressure cooker beeps, allow to naturally release the pressure for 15 minutes then press the valve open to release the remaining pressure.
Lightly separate the meat, or shred if desired retaining all of the juices. Mix with the bell peppers and serve over cauliflower rice, mashed potatoes, a green salad, or in a fresh Italian roll