Preheat your oven to 400°F and line a large baking sheet with parchment paper for easy cleanup.
Peel the pumpkin, sweet potato, and beetroot, then dice them into uniform 1-inch cubes to ensure even roasting.
Mince the garlic clove finely.
In a large mixing bowl, combine the chicken breast and diced root vegetables with the olive oil, minced garlic, rosemary, thyme, sea salt, and black pepper.
Spread the chicken and vegetable mixture in a single layer on the prepared baking sheet.
Roast in the oven for 25 to 30 minutes, or until the chicken reaches an internal temperature of 165°F and the vegetables are tender with golden-brown edges.
While the chicken roasts, place the pumpkin seeds in a small dry skillet over medium heat, tossing frequently for 2-3 minutes until they are fragrant and lightly toasted.
Place the fresh spinach in a serving bowl and top with the hot roasted chicken and vegetables.
Garnish the entire dish with the toasted pumpkin seeds and serve immediately.