Fresh lemon juice adds another layer of flavor to this side dish.
In a small saucepan, heat oil over medium heat. Add onion and carrots; cook, stirring frequently, until onion is lightly browned, about 5 minutes. Add bell pepper and garlic; cook, stirring, until pepper is crisp-tender, about 3 minutes.
Stir in beans, lemon zest, and 1 cup water, and season with salt and pepper; bring to a boil. Reduce to a simmer; cover, and cook until beans have absorbed most of the liquid, about 10 minutes. Stir in lemon juice; season again with salt and pepper.