Heat olive oil in a large pot over medium heat.
Sauté chopped onions until they are translucent, about 5 minutes.
Add minced garlic and sauté for another minute until fragrant.
Stir in the diced potatoes and vegetable broth, bringing to a boil.
Reduce heat and simmer until the potatoes are tender, about 15 minutes.
Add the fresh spinach and cook for an additional 5 minutes until wilted.
Remove from heat and blend the soup until smooth using an immersion blender.
Stir in lemon juice and season with salt and pepper to taste.