Prepare the Tempeh: Place the diced tempeh in a small pot and cover with water.
Bring to a simmer and cook for 10 minutes to soften.
Drain the tempeh thoroughly and set it aside to cool completely.
Make the Dressing: In a medium bowl, whisk together the vegan mayonnaise, lemon juice, garlic powder, Dijon mustard, and sweet pickle relish until smooth and combined.
Combine the Salad: Add the cooled tempeh, green peas, diced celery, and chopped fresh dill to the bowl with the dressing. Gently fold everything together until the tempeh and vegetables are evenly coated.
Chill and Serve: For the best taste, cover the bowl and chill the salad in the refrigerator for at least 1 hour. This allows all the delicious flavors to meld together before serving.