"Fajitas" are a staple in our house; much like "pasta" or "soup." Almost any combination of things can go in them; which is why we usually make them when we're trying to clean out our fridge, or are not feeling culinarily creative, or just want to make a seemingly random assortment of ingredients sound cohesive.
Those were all just big words to say: as long as it tastes good, and maybe looks good, it's all good.