Prep the Sweet Onion: Sprinkle the mandoline-sliced Vidalia onion with a pinch of salt and let sit for 5 minutes to extract excess sharpness and moisture. Rinse 2 to 3 times in cold water.
Then squeeze out all water thoroughly.
Microwave Steam the Kabocha: Wash the kabocha, trim away any bumpy spots on the skin with a knife, and cut into large chunks.
Transfer to a microwave-safe bowl and cover tightly with plastic wrap. Microwave at 600W/700W for 3 to 4 minutes. Let sit covered for 1 minute to finish steaming.
Then carefully unwrap and check with a bamboo skewer to ensure it is fork-tender.
Crisp the Bacon: While the kabocha is microwaving, cut the bacon into 2 to 3 cm chunks and fry in a skillet over medium heat until crispy and golden. Remove the bacon and reserve the rendered fat in the pan.
Combine & Season: In the bowl with the hot microwaved kabocha, add the prepared sweet onion, crispy bacon, mayonnaise, mild curry powder, rice vinegar, and toasted pumpkin seeds. Mash to combine, leaving plenty of rustic kabocha chunks for texture. If you prefer a smoother texture, stir in 1 tbsp of milk.
For extra savory depth, add 1 to 2 tsp of the reserved rendered bacon fat. Season with sea salt and freshly cracked black pepper to taste.
Chill & Serve: Cover and chill in the refrigerator for at least 1 hour (up to overnight) to allow the flavors to meld before serving.