Place trivet in instant pot pan and pour in 1 cup water into instant pot.
Dry chicken with paper towels and remove any pinfeathers. Sprinkle spice mix evenly over chicken and rub it in. Place cut lemon and onion inside cavity of chicken, then place chicken on trivet in instant pot.
Place lid on pressure cooker and be sure valve is turned to sealed.
Set on high pressure for 7 minutes per pound of chicken. For example, for a 3 pound chicken set to 21 minutes on high pressure.
Once cooking time is finished, allow pressure to release naturally for at least 10 minutes, preferably closer to 20 minutes.