Preheat oven to 350 degrees F. Spray a 9x13 pan with nonstick coconut or avocado oil cooking spray.
Season chicken with 1/4 teaspoon salt and 1/4 teaspoon pepper. Set aside
Add 1 tablespoon avocado oil to a large skillet. Heat over medium-high heat until very hot. Toss the broccoli in a skillet and sauté for 30 seconds. Add 1/2 cup chicken broth, cover pan, and lower heat to medium. Steam broccoli until tender about 2 - 3minutes. Transfer broccoli to prepared bake dish in an even layer.
Melt one tablespoon butter (you can substitute with olive oil or avocado) over medium heat. Turn the heat up to medium-high and add chicken in a single layer and sear it. Continue to cook and stir chicken until cooked through. Then evenly layer chicken on top of broccoli.
For the version with dairy: Melt 2 tablespoons butter with 2 tablespoons olive oil over medium heat (or just use olive oil for dair-free version). Whisk in cassava flour and cook, stirring for 1 minute. Turn heat to low, then gradually whisk in 1 1/2 cups chicken broth and 1 cup of milk. Add Worcestershire sauce, and spices.
Bring sauce to a boil, whisking constantly. Reduce heat to a simmer and whisk often until thick. Remove from heat, set it asaide, and whisk in 1 1/2 cup cheddar until melted. Add Parmesan cheese, whisk it until melted. Then whisk the sour cream in until blended. Pour sauce over broccoli and chicken and spread into an even layer.
Cashew sauce: Add all the ingredients to the high- speed blender and blend until smooth. Transfer it to a small pot and cook it for 5 minutes, whisking in occasionally.
Breadcrumbs topping:Melt butter over medium heat in a medium skillet. Add Panko and stir to coat. Continue cooking until crumbs become golden brown.
Pour the sauce over the chicken, broccoli and cheese.
Top it off with breadcrumbs topping.
Put it in the oven at 350 F for 30 minutes.