Spray an 8 by 8 inch pan with cooking spray and set aside.
Select Saute on your instant pot and add the vegetable oil to the pressure cooker. Once it is hot, add the onions and saute for 3 minutes. Add the garlic and sauté for 1 more minute.
Stir in the enchilada sauce, tomatoes with chiles, water, and taco seasoning. Then add the diced chicken and pasta. Lock the lid in place and select High Pressure and 4 minutes cook time.
When the cook time ends, turn off the pressure cooker. Use the quick pressure please. When the valve drops, carefully remove the lid. Select the saute setting and cook for 1 more minute, stirring, until the pasta is tender.
Turn off the Instant Pot and pour the mixture into the square baking dish. Sprinkle the cheese on top. Place under a broiler and broil until the cheese melts and starts to brown.
Serve topped with olives, tomatoes, scallions, and cilantro.