Separate seeds from pulp, rinse well and spread seeds on towel to dry while prepping soup. preheat oven to 375.
Heat oil in large dutch oven or stock pot over medium heat. Add onion (or leek) and cook until beginning to soften. Add garlic, cook until fragrant then add squash and cook until it begins to brown around the edges, 5 -10 minutes. Add brown sugar, red pepper flakes and curry powder, cook a minute or two until fragrant. Add stock until all pieces are submerged (reserve some stock to adjust consistency), bring to boil, reduce heat to simmer and allow to cook until squash is very soft, approximately 20 minutes.
Meanwhile toss seeds with 2 tsp olive oil, 1 tsp garam masala 1/2 tsp salt. Spread in single layer on baking sheet and place in preheated oven. Roast 10-20 minutes until seeds are lightly browned and crisp.
When squash is cooked puree mixture in batches in blender, adding stock as needed for desired thickness, considering whether or not to add coconut milk or heavy cream. Taste and adjust for salt, pepper and curry powder.
Serve warm, garnished as desired.