Season the chicken breast with salt and pepper, sear on both sides in a frying pan over a high heat, then cook in a preheated oven in a foil-covered pan for 25-30 minutes at 180°C (356° F).
For the salsa, add the pickled green tomatoes, diced onion, and jalapenos to a blender and process intermittently until you get a chunky sauce.
Once the chicken is cooked, shred it, and fry in a pan over a high heat with a drizzle of neutral oil. Add the Cajun seasoning and the BBQ sauce and leave for another 1-2 minutes.
Serve on the tortillas with tomatillo salsa and fried onions.