Look for lemongrass paste in the refrigerated produce section, near the packages of fresh herbs. Bonus: One serving of this soup delivers 100% of your daily dose of vitamin A.
Heat oil in a Dutch oven over medium. Add carrots, squash, onion, and salt; cook, stirring occasionally, until softened, about 8 minutes. Add stock, pastes, and ginger; increase heat to high. Bring mixture to a boil. Reduce heat to medium, and cook, covered, until vegetables are very tender, about 15 minutes.
Pour carrot mixture into a blender; add 3/4 cup yogurt. Remove center piece of blender lid (to allow steam to escape); secure lid on blender. Place a clean towel over opening in lid. Process until smooth. Add lime juice; process until combined. Ladle soup into 4 bowls; top evenly with remaining 1/4 cup yogurt and pumpkin seeds.