Soak the beans overnight, or at least 8 hours for best results. Drain.

In a dutch oven or stock pan, heat the olive oil over medium heat. Add the onion and salt and cook until onion is just beginning to soften, about 5 minutes.

Stir in the garlic cloves and cook another minute, then add the vegetable broth. Bring to a boil and add the beans, then reduce heat to low, cover and cook for ~90 minutes, or until beans are softened.

Stir in the spinach and lemon juice and cook for another 5 minutes, until spinach is just wilted. Season to taste.