Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
Peel and cube the sugar pumpkin into 1-inch pieces. Toss with avocado oil, half the sea salt, and half the black pepper.
Spread the pumpkin on the baking sheet and roast for 20-25 minutes until tender and slightly caramelized on the edges.
While the pumpkin roasts, season the chicken breast with the remaining salt and pepper. Heat a large skillet over medium-high heat and sear the chicken for 6-7 minutes per side until the internal temperature reaches 165°F.
Remove the chicken from the skillet and let it rest for 5 minutes before slicing into strips.
Wipe the skillet clean and add the ghee over medium heat. Allow it to melt and begin to foam until it turns a light amber color and smells nutty.
Add the fresh sage leaves and walnuts to the ghee. Fry for 1 minute until the sage is crisp and the walnuts are toasted.
Add the roasted pumpkin and baby spinach to the skillet, tossing gently until the spinach is just wilted.
Plate the pumpkin and spinach mixture, top with the sliced chicken, and drizzle the remaining sage brown butter from the pan over the top.