In a small pot of boiling, salted water, blanch snap peas for 30-40 seconds. Drain and rinse under cold water. Slice into thin strips on the diagonal. Set aside.
In a large pot, heat oil on medium. Add onions and saute' for 6-7 minutes to soften and develop sweetness. Add the red curry paste and saute' for 1 minute. Add the lemongrass, lime peel and lentils. Stir to coat everything well.
Add water or stock and bring to a boil. Lower heat to a bare simmer and cover pot. Simmer for 15 minutes, stirring soup once or twice. Lentils should be completely soft (soup may look a little thick at this point).
Remove lemongrass and lime peels. Blend soup in a blender or with an immersion blender until completely smooth. Put soup back into pot. Add the coconut milk, lime juice, soy sauce and salt. Bring back to a boil for 1 minute and remove from heat. Taste and adjust soy sauce, salt or lime juice, if needed.
Ladle soup into bowls. Garnish with sugar snap peas, cilantro, drizzles of coconut milk and/or chili oil. Serve with extra lime wedges on the side.