Mix all the dry rub ingredients together. Afterward, rub the mixture in the cavity of the turkey breast and all over the exterior of the turkey breast.
Place the onions into the cavity of the turkey breast.
Remove the lid from the Instant Pot, and remove the rack. Next, pour the water into the stainless steel liner.
Place the turkey breast on the rack. Lower the rack into the Instant Pot stainless steel liner using the handles of the rack.
Properly seal the Instant Pot and set the vent to "sealing."
Set the Instant Pot to "high" pressure and set the time for 8 minutes per pound of turkey breast.
Once the turkey breast is finished cooking, allow the Instant Pot to come down from pressure naturally, or release the pressure moving the vent from "sealing" to "venting." BE CAREFUL! If you release the pressure in this way, steam will surge out of the vent. (I prefer to allow the pressure to come down naturally.)
Once the pressure has been released, open the Instant Pot, and remove the lid. Lift the turkey breast out of the stainless steel liner using the handles of the rack. Transfer the turkey breast to a serving platter and enjoy!