Quarter the pumpkin and remove the seeds. Peel and slice into 1-inch cubes.
Add the oil to a large high-sided skillet or Dutch oven over medium-low heat.
Sauté the onions until translucent, about 6 minutes.
Add the pumpkin and continue sautéing for 8-10 minutes, stirring often. Add the peppers, lime leaves, and ginger.
Once the peppers begin to soften, add the garlic, curry paste, and coconut sugar. Stir for a few minutes, until very fragrant, then add the fish sauce.
Simmer for 5 minutes, then slowly stir in the coconut milk and cashews.
Allow the curry to simmer gently, stirring often and reducing the heat as needed, until the pumpkin is fork-tender. Just before serving, add the juice of 2 limes.
Serve the curry over rice and top with cilantro and scallions.