If using dry Pinto beans, soak them overnight and then cook them the next day. Rinse rice under running water till the water runs clear. You can also add it without rinsing.
Add butter and oil to the Instant Pot. Turn it on to saute mode. Fry minced serrano peppers, garlic, white part of scallions and chopped onions.
After the onions have turned translucent, add the chopped bell peppers and sweetcorn. Saute for a minute.
Add the rinsed rice to the pot.
Then add red pepper flakes, oregano, cumin powder, Taco seasoning, and Mexican seasoning mix (if adding). Mix and saute the rice for a minute.
Now add water, scrape all the sides and give it a stir.
Next, add the salsa in the center. Do not mix it. Cancel the saute mode. Close the lid. Cook in manual/pressure mode for 4 minutes.
Release pressure naturally after 10 minutes. Fluff the rice with a fork. Let it sit for about 5 minutes. Then add the canned pinto beans.
Garnish with green part of scallions and cilantro. Mix them all with the rice lightly. Check and add salt.
Serve it with shredded lettuce, crushed tortilla chips, shredded cheese, sour cream.