If using the oven, preheat to 400°F (200°C). If using an air fryer, skip this step.
Carefully cut the kabocha squash in half, scoop out seeds, and lightly coat cut sides with avocado oil.
Air Fryer: Place squash cut-side up in basket, air fry at 390°F (200°C) for 20 mins until tender. Oven: Place cut-side down on parchment-lined sheet, roast at 400°F (200°C) for 45 mins until tender.
While squash cooks, heat avocado oil in a soup pot over medium heat. Add chopped yellow onion and a pinch of salt; sauté until translucent (about 5 mins).
Add minced garlic and sauté for 1 minute more, lowering heat if needed to prevent burning.
Stir in curry powder, cumin, and chopped apple. Deglaze the pot with water and Better Than Bouillon base. Cover and simmer on low for 7-10 minutes.
Once squash is cooked, remove from heat. Chop the flesh into medium pieces, discarding the stem and tough parts of the peel.
Add the chopped kabocha squash flesh to the soup pot.