Preheat your oven to 400°F (200°C). Place the chicken thighs on a large baking dish and season with salt, pepper, dried thyme, and 1 tablespoon of olive oil. Roast in the oven for about 20 minutes until the skin is crispy and the meat is starting to brown.
While the chicken roasts, toss the cubed sweet potatoes and sliced onion with a tablespoon of olive oil, salt, and pepper. Spread them out on a baking sheet and roast for 20 minutes, stirring halfway through, until tender and caramelized.
Remove both dishes from the oven; the chicken should have golden skin, and the vegetables should be soft and caramelized. Spread the sweet potatoes and onions evenly in the casserole dish, creating a bed for the chicken.
Place the chicken thighs on top of the bed of roasted vegetables. In a small bowl, mix the remaining olive oil with the minced garlic and a pinch of salt. Drizzle this over the chicken to infuse flavor.
In a small bowl, combine the breadcrumbs, Parmesan cheese (if using), and ground cinnamon. Sprinkle this mixture evenly over the entire casserole for a crunchy, fragrant topping.
Bake the assembled casserole in the oven for another 10–15 minutes, until the topping is golden brown and crispy, and the dish is bubbling around the edges.
Remove from the oven and let rest for a few minutes. Garnish with fresh herbs if desired. Serve hot and enjoy the warm, hearty flavors with a comforting crunch in every bite.
