1. Prepare the Tempeh: Slice the tempeh into small cubes or crumble it, depending on your texture preference.
2. Cook the Tempeh: In a skillet over medium heat, sauté the tempeh for about 5-7 minutes until it is golden brown.
3. Mix the Salad: In a large bowl, combine the cooked tempeh, celery, red onion, vegan mayonnaise, and Dijon mustard. Mix until everything is well coated.
4. Season: Add salt and pepper to taste, adjusting based on your preference.
5. Assemble the Sandwich: Spread the tempeh mixture onto whole grain bread or in lettuce leaves for a low-carb option.
6. Serve: Enjoy your tempeh chicken salad sandwich fresh with your favorite sides or make it ahead for later!

By following these straightforward steps, you’ll create a delicious, plant-based sandwich sure to impress your taste buds.