Preheat your oven to 375°F (190°C). Place sweet potatoes on a baking sheet, toss with a tablespoon of olive oil, and season with salt and pepper. Roast for about 25-30 minutes until tender and slightly caramelized.
While the sweet potatoes roast, season the chicken breasts with salt, pepper, and half of the crushed sage. Heat a tablespoon of olive oil in a skillet over medium heat and cook the chicken until golden and cooked through, about 6-8 minutes per side. Let cool slightly, then shred with forks or chop into bite-sized pieces.
Once the sweet potatoes are done, add them to a large mixing bowl along with the shredded chicken. Drizzle with a little more olive oil if needed and mix gently to combine.
Transfer the mixture into a baking dish, spreading it out evenly. Sprinkle the remaining sage and shredded cheese over the top to add flavor and melt into the casserole as it bakes.
In a small bowl, combine the breadcrumbs and melted butter, then sprinkle evenly over the cheese layer for a crispy topping.
Bake in the preheated oven for 20-25 minutes until the top is golden brown and bubbling around the edges. The house will fill with warm, savory aromas as the cheese melts and the topping crisps up.
Remove from the oven and let rest for a few minutes before serving. The casserole should be hot, with a crispy topping and a hearty, fragrant filling.
