Preheat the oven to 375°F (190°C).
Cut the top off the small pumpkins and scoop out the seeds and pulp to create a bowl. Roast the pumpkin bowl in the oven for about 20-25 minutes until slightly softened.
In a large pot, combine the pumpkin puree, coconut milk, vegetable broth, Thai red curry paste, ginger, garlic, lemongrass, soy sauce, and brown sugar. Bring to a simmer over medium heat.
Let the soup simmer for about 15-20 minutes, stirring occasionally.
Stir in the lime juice and season with salt and pepper to taste.
Carefully ladle the hot soup into the roasted pumpkin bowls.
Garnish with fresh cilantro and red chili slices.
Serve the Pumpkin Thai Soup hot and enjoy!