Season steak strips generously with salt and pepper.
Heat a cast iron skillet on medium until extremely hot (but not smoking).
Add oil to pan and swirl around until shimmery.
Add steak to pan and let brown, stirring often. Steak should cook quickly if heat is high enough, so stir often to prevent sticking or burning.
When steak is browned (after about 2 minutes) - but not cooked through - add onions and peppers.
Let steak, peppers, and onions cook until vegetables are browned and soft and steak is cooked through, about 4 minutes.
Sprinkle seasoning mix over chicken and vegetables and stir to coat, adding lime juice to help coat. Add up to 2 tbsp water if needed to spread seasoning more evenly.
Turn off heat and sprinkle with cilantro. Serve immediately.