Heat the oil in a large saucepan over medium heat.
Add the onion and garlic and cook, stirring, for about 5 minutes until softened.
Add the green onions and okra and stir for 1 to 2 minutes.
Pour in the broth and lemon juice, then season with salt and pepper.
Bring to a boil, then reduce the heat, cover, and simmer for 30 minutes, until the okra is very tender.
Stir in the chopped coriander.
Blend until smooth, using an immersion blender or by working in batches in a countertop blender. Let the soup cool slightly first, and vent the lid when blending hot liquid.
Taste and adjust the salt, pepper, and lemon. Serve warm.