Preheat oven to 275 F and line a baking sheet with parchment paper.
Add the cauliflower rice to a microwave-safe bowl and microwave according to package directions. Let cool.
Squeeze out as much liquid as possible from the cauliflower, using a dish towel to wring out the moisture. Add to a food processor and pulse until finely chopped.
Transfer the cauliflower to the prepared baking sheet and bake for 1 hour until, stirring every 20 minutes, until dried out and crispy. Let the cauliflower cool. Meanwhile, increase the oven temperature to 400°F.
Transfer cooled crispy cauliflower to a shallow bowl and add parsley, onion powder, garlic powder, ground mustard, grated parmesan, salt, and pepper. Toss to combine.
Add eggs and buttermilk to another shallow bowl and beat to combine.
Pat the chicken tenderloins with paper towels so that they are dry. Dip the chicken in the egg wash, then the cauliflower breadcrumbs, pressing to adhere. Place on a parchment-lined baking sheet.
Bake for 15 minutes, flipping halfway through. Serve with your favorite dipping sauce.