Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Carefully slice the kabocha squash in half, remove the seeds with a spoon, and cut the flesh into 1-inch cubes.
Place the squash cubes and the chicken breast onto the prepared baking sheet.
Drizzle the olive oil over both the chicken and the squash pieces.
In a small bowl, mix the sea salt, black pepper, rosemary, thyme, and garlic powder together.
Sprinkle the herb mixture evenly over the chicken and squash, tossing the squash to ensure every piece is well-coated.
Roast in the oven for 25 to 30 minutes, flipping the squash cubes halfway through, until the chicken reaches an internal temperature of 165°F.
Remove from the oven and let the chicken rest for 5 minutes before slicing it into strips.
Serve the herb-crusted chicken alongside the tender roasted kabocha squash.