Heat oil in heavy large pot over medium-high heat. Add green onions, garlic, thyme, and chile. Sauté until soft, about 2 minutes. Add broth, pumpkin, ham, and okra. Bring to boil; reduce heat to medium and simmer until vegetables are tender, stirring occasionally, about 10 minutes. Add callaloo; cook until wilted and leaves are tender, stirring frequently, about 3 minutes. Season to taste with salt and pepper.