Lightly spray the skirt steak with avocado oil spray and generously coat it in fajita seasoning. Repeat for both sides.
Spray a heavy bottomed skillet with avocado oil spray and heat over medium-high heat. Add the skirt steak and sear quickly on both sides. Don't cook it through, you're only looking to sear it.
Add the skirt steak to a sheet pan along with the onion, poblano, and bell peppers.
Spray them with avocado oil spray and sprinkle lightly with salt, pepper, and the remaining fajita seasoning.
Place the baking sheet in the oven for 15-20 minutes depending on how well done you would like your skirt steak.
Remove the baking sheet from the oven and allow the steak to rest before slicing. Be sure to slice against the grain and enjoy in warm tortillas.