In a medium saucepan, heat oil over medium. Add scallions, garlic, and oregano; cook, stirring frequently, until scallions begin to soften, about 3 minutes.
Stir in broth and beans; cook until heated through, about 4 minutes. Using a wooden spoon or potato masher, lightly mash some of the beans to thicken the soup. Stir in lemon juice; season with salt and pepper. Before serving, sprinkle with Parmesan.
To store, refrigerate in an airtight container, up to 3 days.