Place trivet in Instant Pot. If using a 6-quart Instant Pot, pour in 1 cup water. If using an 8-quart Instant Pot, pour in 1 ½ cups water.
Trim approximately ¼-inch from top of bell peppers, then remove stems, ribs, and seeds. Salt insides of bell peppers, then place empty peppers on trivet inside instant Pot.
In medium bowl, mix together ground beef, Italian seasoning, salt, garlic, tomato sauce, and diced tomatoes, until mostly combined. Add in rice and 1 cup shredded cheese. Gently combine mixture, then spoon filling into peppers.
Secure lid on Instant Pot and set to Manual High Pressure for 9 minutes. Instant Pot will take approximately 10 minutes to come to pressure, then 9 minute cook-time will start.
When cook-time is finished, carefully turn venting knob to quick release pressure.
Remove lid. Sprinkle remaining cheese on tops of bell peppers. Return lid to pot and allow cheese to melt.
Using tongs, carefully remove peppers from Instant Pot. Garnish with fresh parsley if desired and serve immediately.