Preheat the oven to 400°F. In a large oven-safe skillet, melt 1 tablespoon of butter over medium-high heat. Add the bread crumbs and stir quickly to coat. Saute with stirring frequently for about 2 minutes, until toasted. Remove from the heat, transfer to a plate, and let cool.

In the same skillet, melt the remaining butter over medium-high heat. Add the flour and whisk to combine. Slowly add the chicken stock, whisking until smooth. Reduce heat to medium-low and simmer for a few minutes, until thickened. Whisk in the cream along with the garlic powder and cayenne pepper.

Remove from the heat. Stir in the mushrooms, broccoli, and rice. Add half of the cheese and stir to mix throughout. Taste and add salt and pepper, as needed. Top with the remaining cheese and sprinkle with the toasted bread crumbs. Bake until lightly browned and bubbly, about 18-22 minutes. Sprinkle with parsley and serve warm.