Heat the oil in a large pot over medium-low heat. Add the shallots and cook for 4 minutes. Add the garlic and greens and cook, stirring frequently, until the greens begin to wilt, 3 to 5 minutes. Add 1 tablespoon of the lemon juice, the brown sugar, bay leaf, red pepper, broth, and tomatoes and their juices. Bring to a boil. Reduce heat and simmer gently until the greens are tender, about 15 minutes. Add the beans and cook for 5 minutes. Remove and discard the bay leaf. Season with the salt, black pepper, and (if desired) the remaining lemon juice.