Have all ingredients ready and measured. Have red peppers roasted, cooled, remove the skins, and chop. Make pumpkin puree (or use canned). Juice a lemon (or use pre-bottled).
Heat butter or oil in a 4-quart (or larger) soup pot over medium-high.
Add onion and cook, stirring, until golden, 8-10 minutes.
Add garlic and cook an additional 2 minutes.
Add turmeric, paprika, and chili flakes; stir.
Add pumpkin puree, broth, peppers, and peanut butter; whisk to incorporate and bring to a boil.
Reduce heat, simmer for 5 minutes, then stir in sugar, salt, pepper, and lemon juice. Remove from heat.
Using an immersion blender, carefully puree until smooth. Alternately, let soup cool down a bit before pureeing in small batches in a regular blender.
Divide among 4 bowls and garnish with sour cream, peanuts, reserved chopped roasted red peppers, and scallion greens.