Preheat the oven to 400 degrees.
Prepare a baking sheet with a silicone baking mat or parchment paper.
Remove the core and leaves from the base of the head of the cauliflower.
Cut the cauliflower into florets that are similar in size.
Place the cauliflower florets on the baking sheet.
Sprinkle the cauliflower florets with 2 Tablespoons of garlic powder.
Cook for 30 minutes.
Remove the cauliflower from the oven and allow to cool to the touch.
Transfer the cooked and cooled cauliflower to a cutting board and roughly chop.
Transfer the cut cauliflower to a large bowl.
Add the chopped celery, green onions, dill pickles, and dill.
Combine the cashew mayo, yellow mustard, lemon juice, salt, and pepper in a small bowl.
Whisk together.
Pour the mayo/mustard dressing into the bowl with the vegetables.
Stir to combine the ingredients with the dressing.
Cover the salad and refrigerate for at least 30 minutes before serving.