Start by patting the sirloin steak or flank steak dry with paper towels. This helps achieve a nice sear. Season the meat generously with 1 tablespoon of fajita seasoning, ensuring it's evenly coated.
Turn the Instant Pot to the 'Sauté' mode and add 1 teaspoon of olive oil. Once the oil is hot, add the seasoned steak. Sear it for about 3-4 minutes on each side until it’s browned.
Pour in 1 cup of low-sodium beef broth to deglaze the pot, scraping any brown bits off the bottom. Secure the lid and set the Instant Pot to 'Manual' for 10 minutes.
While the steak is cooking, slice the onion and bell peppers. In a small bowl, toss the sliced vegetables with 1 tablespoon of fajita seasoning to coat them evenly.
Once the cooking time is up, perform a quick release of the pressure. Open the lid carefully. Remove the steak and let it rest for a few minutes before slicing it into thin strips against the grain.
Add the seasoned bell peppers and onion to the Instant Pot. Stir to combine with the remaining juices. Select 'Sauté' mode again and cook for 5-7 minutes, or until the vegetables are tender but still crisp.
Return the sliced steak to the pot, stirring to mix everything together. Finish by adding the lime zest and juice from the two limes, stirring well to incorporate. Serve hot with tortillas or over rice.
