Set your Instant Pot to the sauté setting, and place the chicken breasts in the bottom of the stainless steel pot. Season the chicken breasts with garlic salt and seasoned pepper and brown on both sides for 6 or 7 minutes, or until golden brown. When chicken breasts have been sautéed on both sides, turn off the sauté setting. Add the onion slices, crushed pineapple, including the juice, brown sugar, soy sauce, and BBQ sauce. Stir ingredients to blend, and place lid on INSTANT POT until it beeps and locks. Make sure the Valve is turned to 'Sealing' or 'SEAL', and push the POULTRY button on the Instant Pot. Let chicken cook until the Instant Pot beeps, and goes to the 'KEEP WARM' setting. Let the Instant Pot automatically build and release the pressure for this dish. Once the Keep Warm button is on, and the counter begins to count up, make sure the Valve is all the way down, and with a pot holder, turn the Valve to release, just to make sure the pressure is completely released. Remove the lid from the Instant Pot, and stir the chicken. Let the chicken cool a bit, and then shred chicken with two large forks, and toss in sauce.