Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper for easy cleanup.
Dice the chicken breast into uniform 1-inch cubes and peel and cube the butternut squash into similar 1-inch pieces.
In a large mixing bowl, combine the chicken, squash, olive oil, finely chopped fresh sage, sea salt, black pepper, and garlic powder.
Toss everything thoroughly until the chicken and squash are evenly coated in the oil and seasonings.
Spread the mixture across the prepared baking sheet in a single layer, ensuring the pieces are not overcrowded so they roast rather than steam.
Roast for 20 to 25 minutes, tossing the ingredients halfway through, until the squash is fork-tender and the chicken reaches an internal temperature of 165°F.
Remove from the oven and serve immediately, garnishing with a few extra leaves of fresh sage if desired.