Select Sauté and add 2 tablespoons oil or butter to the pot. Add the onions, celery, bell pepper, and ¼ teaspoon salt. Cook for about 5 minutes, until the vegetables soften and the onion is translucent.
Measure 1½ cups cooked turkey, preferably thigh meat, and chop into small, bean-sized pieces. Use the measured amount rather than a set number of thighs.
Turn off Sauté. Add the peas, cooked turkey, cornbread, stuffing mix, ground sage, poultry seasoning, and all 3 cups stock. Mix well. Keep the separate cup of water out of the dressing mixture.
Coat a 7-inch broiler-safe pan with nonstick cooking spray. Transfer the dressing to the pan, spread evenly, and pack down firmly. Cover with aluminum foil.
Without rinsing the cooker pot, add 1 cup water and the 3-inch trivet. Place the covered pan on the trivet, lock the lid, and cook at High Pressure for 30 minutes. Quick release the pressure, then wait until the cooker is fully depressurized before opening.
Carefully lift out the hot pan with oven mitts and remove the foil. Broil on High for about 5 minutes, watching closely, until the top is browned and crisp.
Check that the center reaches 165°F before serving; this dressing contains cooked turkey.