Preheat oven to 375° F
Place on a parchment lined baking sheet. Bake at 375° F for approximately 45 minutes until slightly softened. (time will depend on actual size of the pumpkin). Remove from heat and carefully remove lid and set aside to cool slightly.
Using a sharp knife, remove top from pumpkin in one piece and set aside. Remove seeds and stringy pulp from inside pumpkin using a spoon or scoop. Replace lid on pumpkin.
Meanwhile while pumpkin is roasting, toast walnuts in dry skillet 5-6 minutes over medium heat until fragrant. Stir often and watch carefully to prevent burning. Remove from heat and set aside.
Add oil in large deep skillet. Add onion. Cook, stirring occasionally, until onions become slightly soft and translucent.
Add diced chicken and saute’ until golden brown.
Add garlic, tomato puree, and water. Cover skillet with a lid and simmer over low heat for approximately 20 minutes.
Ladle filling into pumpkin. Add chopped walnuts, herbs, and cherry tomatoes, reserving a few for garnish. Season with salt and pepper to taste.
Return pumpkin to oven and roast for another 20-25 minutes.
Serve warm.