In the liner of the Instant Pot add the chicken broth, diced onion and garlic powder, stir to combine.
Add the chicken breasts (sliced horizontally in half if large chicken breasts) in the liquid.
Pour the can of Fire Roasted tomatoes on top of the chicken, do NOT stir.
Add the lid and place valve in the Sealing position. Pressure Cook/Manual on HIGH pressure for 10 minutes. After the cooking time expires, allow for Natural Pressure Release for 10 minutes then release any remaining pressure.
Remove chicken breasts to a cutting board and shred. Remove the liquid from the liner of the Instant Pot and clean pot.
Assemble the Enchilada Casserole
Spray a springform or push pan with non-stick cooking spray.
Cut the 9 tortillas in half. Using 6 halves (3 whole corn tortillas) layer the bottom of the springform/push pan, overlapping when necessary.
Add ½ of the shredded chicken to the top of the tortillas. Then add 1/3rd of enchilada sauce and 1/3rd of the shredded cheese.
Repeat with another layer of 6 tortilla halves, ½ chicken, 1/3rd enchilada sauce, 1/3rd shredded cheese.
Assemble the final layer of 6 tortilla halves and 1/3rd enchilada sauce. Do not add the final layer of cheese.
Loosely cover the top of the springform/push pan with foil.
Add 1 cup of water and a trivet to the liner of the Instant Pot.
Using a trivet with handles (or silicone sleeve or aluminum foil sling) carefully lower your pan into the pot and placed on the trivet.
Lock the lid in place with the valve in the Sealing position. Pressure Cook/Manual on HIGH pressure for 10 minutes. Once cooking time is up, Quick Release the pressure.
Carefully lift the pan out of the Instant Pot and remove the foil. Add the remaining cheese.
Place the pan back into the Instant Pot and add the lid (no need to lock the lid). Let Enchilada Casserole sit for 5-10 minutes to allow the cheese to melt and the casserole to set.
Serve warm with any suggested toppings: cilantro, guacamole, sour cream, green onions, etc..