Marinate Chicken: Add all the ingredients in a bowl mentioned above in the "seasonings for chicken" along with the diced chicken cubes. Mix well until all the chicken pieces are well coated with the marinade. Rest for 30 mins.
Sear Chicken: Set the Instant Pot on SAUTE function & set it on HIGH heat. Add oil, when the oil becomes moderately hot gently release the marinated chicken pieces and sear until they become golden around the edges. Set the seared chicken pieces aside.
Saute Aromatics: Now, add butter and allow it to melt. Than. throw in the chopped onion and bell peppers. Saute for 1 min. Add salt and mix well. Add the garlic and saute another 30 secs. Next, add the cumin, chili powder & paprika mentioned in the "seasonings for rice" above (do not add the fajita seasoning now). Saute another 30 seconds.
De-glaze pot: Pour the chicken stock and de-glaze the pot very well scraping the sides & the bottom of the pot with the help of a spatula. There should not be any food particles stuck at the bottom of the pot. This will prevent the burn. Turn off the SAUTE function.
Layer ingredients: Add the corn and black bean, give a quick stir. Rinse the long grain white rice very well under running tap water until clear water runs through. Drain the rice very well in a colander and than add it to the pot. Gently spread the rice with the help of a spatula and push it down. DO NOT stir or mix. It's ok if the rice is not below the liquid. Next, pour the diced fire roasted tomatoes and spread them out on top of the rice. DO NOT mix or stir. Add the fajita seasoning now. Transfer the seared chicken pieces into the pot and spread them out on top of the tomatoes. DO NOT stir or mix.
Pressure Cook: Secure the lid of the instant pot, seal the valve and PRESSURE COOK on HIGH for 6 mins. Once, the cooking cycle is over the instant pot will begin to beep. Wait for 5 mins Natural Release and than release the rest of the pressure manually by moving the valve from the sealing to the venting position. Open the lid when the metal pin drops. Gently fluff the fajita rice with the help of a pair of fork. The rice will look moist at this super hot stage but it'll retain a perfect texture as it cools down.
Add Cheese: Now, add the lemon juice and ½ cup shredded Mexican cheese and mix gently. Add the rest of the 1 cup Mexican Cheese, DO NOT mix or stir. Cover the Instant pot with a temporary glass lid or the instant pot lid and rest for 5 mins. This will allow the cheese to melt. Serve hot with your favorite toppings like - diced avocados, cilantro, lime wedges, sour cream, chopped tomatoes. Enjoy!