In a medium bowl, add the mayonnaise, Dijon mustard, red wine vinegar, and a pinch of salt and black pepper, and whisk until well combined.
To the same bowl, add the lettuce, salmon, celery, red onion, dill, and cucumber, and toss until well coated in the dressing. Taste and adjust seasoning with salt and pepper to taste.
If you prefer a warm pita, you can warm your pita in an oven at 350°F for a few minutes or in the microwave for 10-20 seconds.
Place the pita on a cutting board, slice it in half, and open each side to create a pocket. Then fill each side of the pocket with sliced tomatoes and the salmon salad mixture.