Set your Instant Pot to Sauté and add the olive oil. Once heated (about 2 minutes), add the lean ground beef, season with salt and pepper, and cook until browned (around 5 minutes). Drain excess grease if needed.

Add the diced onion, green bell pepper, and minced garlic to the pot. Sauté for about 2 minutes until the vegetables are softened and fragrant.

Sprinkle in the soy sauce, Worcestershire sauce, and brown sugar, scraping up any brown bits from the bottom of the pot. Then add the tomato paste and carefully layer the ketchup and Dijon mustard over the top along with water. Do not stir so the flavors remain distinct.

Seal the Instant Pot, set it to Pressure Cook on High for 5 minutes, and then allow a 10-minute natural pressure release. Open the lid carefully once finished.

If the sauce seems too runny, switch to Sauté mode and simmer until it thickens to your liking. Adjust salt and pepper if needed. Serve the sloppy joe mixture on your toasted burger buns.