Using the saute function, heat the oil in the pressure cooker. Add the fennel, onion, and salt, and cook until the vegetables have just softened, 5 minutes. Add the squash and coriander and cook, stirring occasionally, until the vegetables are starting to turn golden at the edges, 7 to 10 minutes.
Add the stock, cover, and cook on high pressure for 20 minutes. Let the pressure release naturally.
Using an immersion blender directly in the pot or transferring the soup to a blender, puree the soup with the lemon zest until smooth. Season with salt, pepper, and lemon juice to taste. Serve garnished with the fennel fronds, cilantro, and a drizzle of olive oil.
Buy pre-peeled, chopped butternut squash for even easier prep.