Select the Saute setting on your Instant Pot and heat the oil.
Add the pancetta and cook until starting to become <g class="gr_ gr_113 gr-alert gr_gramm gr_inline_cards gr_run_anim Punctuation only-del replaceWithoutSep" id="113" data-gr-id="113">crisp,</g> about 3 minutes.
Add the onion and garlic to the pot and saute for another 3 minutes, until onions are soft.
Add the tomatoes with their liquid, wine, stock tomato paste, salt and pepper, oregano, basil, red pepper flakes, and bay leaf, and stir with wooden spoon.
Add the chicken to the pot and nestle the chicken into the sauce.
Secure the lid and set the Pressure Release to Sealing.
Press the Cancel button to reset the cooking program, then select the Poultry (or Meat/Stew) setting and set the cooking time for 12 minutes at high pressure.
Perform a quick release by moving the Pressure Release to Venting, or let the pressure release naturally.
Open the pot. Use a slotted spoon to transfer the chicken to a cutting board.
To reduce the sauce, press the Cancel button and then select Saute and cook the sauce for about 12 minutes longer.
Meanwhile, use two forks to shred the cooked chicken.
Once the sauce has thickened somewhat, removed the bay leaf and add the shredded chicken back to the sauce.
Butter the buns and toast them under the broiler for about 1 minute, until lightly toasted.
Place a couple strips of roasted red pepper on each bottom half of the buns.
Use tongs to place about 1 cup of the pulled chicken onto the red pepper.
Top with cheese. At this point, you can return to the broiler to quickly melt the cheese, if desired.
Top with remaining bun tops.