Preheat a grill or grill pan on medium heat.
Season the steak on both sides well with steak seasoning, salt, and pepper.
Heat the oil in a nonstick pan over medium heat. Saute the peppers and onions until soft, approximately 6 - 8 minutes. Remove from the heat, cover with a lid and set aside.
Cook the steak on both sides to your desired temperature using a thermometer. (see below) Once done allow the steak to rest on a cutting board for 3 - 5 minutes before slicing against the grain into thin slices.
In the meantime. Place the yogurt, cucumber, red onion, garlic, lemon juice, and dill in a blender. Blend until smooth. Season with salt and pepper to taste.
Warm the pita on both sides on a medium heat grill or in a saute pan for approximately 30 seconds per side.
Place the onions, peppers, lettuce, tomato, and sliced steak on the pita. Drizzle the sauce over top, garnish with cilantro and serve.