Marinade the Pork: Combine the soy sauce, lime juice, maple syrup and sesame oil in a large resealable plastic bag. Add the prepared tenderloin. Close bag, pressing out the air. Flip a few times to coat the pork in the marinade. Place in the refrigerator and let marinade 2-8 hours. When ready to cook, remove tenderloin from marinade and discard marinade. Season lightly with salt and freshly ground pepper.
Cook the Pork: Preheat oven to 375°F. Heat oil in a large ovenproof skillet over medium-high heat. Sear tenderloin in hot oil, turning as needed, until browned on all sides, about 5 minutes. Transfer skillet to oven and roast until an instant-read thermometer inserted into the thickest part of tenderloin registers 135 - 140F, 10-15 minutes. Transfer pork to a cutting board and let rest at 5 minutes before slicing.
Prepare the sauce: While the pork is cooking, heat 1 Tbsp. oil in a large saucepan over medium heat. Cook shallot and garlic, stirring regularly, until softened, about 3 minutes. Add the curry paste and cook, stirring constantly, until paste is slightly darkened in colour and very fragrant, about 2 minutes. Add the coconut milk, lime zest, brown sugar and lime juice and stir to combine. Bring to a simmer and continue simmering until reduced and thickened.
To Serve: Slice pork in to 1/4-inch slices and arrange on a a deep serving platter. Spoon warm sauce overtop. Garnish with chopped cilantro and pumpkin seeds. Serve with rice, if desired.
Be sure to scroll up to read the Ingredient Notes and Cook's Notes, for more helpful tips, substitution suggestions and suggested variations and/or serving suggestions for this recipe.