Wash bell peppers. Remove stem (cutting JUST around the stem) and slice horizontally (see notes above). Remove seeds and membranes.
Combine remaining ingredients in a large bowl (except shredded cheese for garnish) and mix until well combined.
Divide mixture evenly between the 8 halves (it's ok if they are heaping).
Place trivet in Instant Pot and pour in 1 cup water, covering the bottom of the Instant Pot. Place 4 of the stuffed peppers onto the trivet (I did this in my 6qt).
Now, you can cook them 4 at a time OR you can cook them all at once if you place the trivet with handles with the handles DOWN making kind of a table over the other trivet and first layer of peppers-- the "table" will seem wobbly or lean to one side but it won't fall over, it has nowhere to go. Place the remaining 4 stuffed peppers over the top.
Place the lid on the Instant Pot and seal, placing the tab to "sealing". Manually cook on high pressure for 9 minutes. Slow release for about 1-2 minutes and then quick release.
Open the Instant Pot and place cheese over all of the stuffed bell peppers (if you did 2 layers with the 2 trivets do this carefully removing the top layer and adding cheese to all the peppers and putting the top layer back).
Place lid back on Instant Pot for about 3-5 minutes or until cheese has melted. Serve hot.