In a small bowl, combine the ingredients for the fajita mix, chili powder, ground cumin, paprika, garlic powder, onion powder, cayenne pepper and kosher salt.
Heat 1 tablespoon of olive oil in a large skillet over medium-high heat. When hot, place the strips into the skillet, ensuring not to overcrowd. Cook for 2-4 minutes until medium rare.
Pour another tablespoon of olive oil into the same skillet. Add the onions and peppers, cooking about 3 minutes until softened. Season with the remaining fajita seasoning.