Heat oil over medium-high heat in a large saucepan. Add shallot, garlic, and ginger, and stir-fry until fragrant, about 1 minute.
Reduce heat to medium. Add the red curry paste and stir to break up, about 1 minute. Add pumpkin, and stir-fry another minute, mixing it well with the curry paste and aromatics.
Add coconut milk, stock, fish sauce, lime juice, pepper (if using) and sugar. Bring to a gentle boil. Reduce heat to medium low and simmer 10-15 minutes, until pumpkin is fork tender.
Add prawns and simmer until cooked through, about 3 minutes.
Serve with rice. Garnish with cilantro and lime wedges.
Notes
You can also use maple syrup in place of brown or palm sugar