Preheat the oven to 425°F.
Arrange the chicken pieces on a baking sheet. Coat them with 1½ tablespoons of oil, then season with salt and pepper.
Line a separate baking sheet with parchment paper and spread the broccoli florets over it. Toss the broccoli with 1½ tablespoons of avocado oil, then season with salt and pepper.
Roast the chicken for 20–25 minutes, turning the pieces halfway through so they cook evenly and are fully done.
At the same time, roast the broccoli for 15–20 minutes, stirring midway through cooking, until the florets are tender when pierced with a fork.
After roasting, reduce the oven temperature to 400°F.
While the chicken and broccoli cook, place the bacon in a large skillet and cook until crisp. Transfer it to paper towels to drain, then reserve it for the topping.
To prepare the sauce, warm a medium saucepan over medium heat and add the 3 tablespoons of ghee.
Add the finely diced onion and cook until translucent and aromatic. Stir in the minced garlic and continue cooking until softened, lowering the heat when necessary to prevent scorching.
Whisk the tapioca flour thoroughly into the chicken broth. Pour this mixture into the saucepan.
Immediately whisk in the coconut milk, spicy brown mustard, and nutritional yeast.
Increase the heat and bring the sauce to a boil while stirring continuously.
Once boiling, reduce the heat to a gentle simmer. Continue stirring and cooking for approximately 1 minute, or until the sauce noticeably thickens.
Season with the sea salt and black pepper, then mix in the rosemary and sage.
Stir the cauliflower rice into the sauce and allow it to begin softening. Remove the saucepan from the heat.
Cut the roasted chicken into smaller bite-size portions if necessary, or shred it.
Transfer the cooked chicken to a casserole dish. Add the roasted broccoli followed by the cauliflower rice and sauce mixture. Stir carefully until all ingredients are evenly coated and distributed.
Crumble the crisp bacon over the surface of the casserole.
Bake uncovered at 400°F for approximately 20 minutes, until the casserole is thoroughly heated and the cauliflower rice has become tender.
Serve the chicken casserole hot.