Prepare the Pancetta: Heat the olive oil in a cast iron or soup pot over medium heat. Add the pancetta and cook until browned and crispy. Remove the pancetta with a slotted spoon and set aside, leaving about 2 tablespoons of bacon fat in the pot.
Sauté Vegetables: Add the diced onion, carrots, celery, and garlic to the pot. Cook, stirring occasionally, until the vegetables begin to soften.
Add Herbs and Lentils: Stir in the fresh rosemary, dried oregano, and thyme. Add the green lentils and quartered mini potatoes, stirring to coat them in the bacon fat and mix with the vegetables.
Simmer the Soup: Pour in the vegetable stock and bring to a boil. Reduce the heat to a gentle simmer and cook for about 20 minutes, or until the lentils are tender.
Blend for Creaminess: Place about one-third of the soup in a blender and blend until smooth. Return the blended portion to the pot and stir well to incorporate.
Finish the Soup: Add the lemon juice and baby spinach, stirring until the spinach wilts. Return the cooked pancetta to the pot and mix well.