Preheat the oven to 375° F. Line 2 large baking sheets with parchment.
Place the cauliflower on the prepared baking sheet and drizzle with olive oil. Season with salt and pepper. Toss together to make sure the cauliflower is evenly coated and spread into a single layer. Roast the cauliflower in the oven for 30-35 minutes, until the florets just begin to brown and are fork tender. Allow cauliflower to cool while you prepare the remaining ingredients.
In a large bowl, combine mayo, mustard, chopped dill pickle and pickle juice, celery, green onion and chopped hard boiled eggs. Add cauliflower and mix everything together. Taste and season with more salt and pepper to your preference. Top with crumbled bacon. Refrigerate for at least 30 minutes before serving.
Store in an airtight container in the refrigerator and enjoy within 3 days.