Heat a Dutch oven or soup pot over medium heat for about 1 minute, then add the oil and swirl to coat.
Add the onion, chili powder and cumin and cook for 5 minutes, stirring often.
Add the bell pepper, chiles (to taste), garlic and 1 teaspoon of salt, and cook, stirring occasionally, until softened, about 5 minutes.
Stir in the potatoes and the remaining ½ teaspoon of salt.
Reduce the heat to low, cover and cook for about 5 minutes, stirring once or twice.
Add the bean cooking liquid or water, cover and cook until the potatoes are tender but not mushy, 15 to 30 minutes. Add more cooking liquid or water if the mixture seems dry.
Gently stir in the beans, along with the tomatoes and their juices.
Raise the heat to medium-high and bring to a boil; then reduce the heat to medium-low and cook, uncovered, until warmed through, about 5 minutes.
Taste, and season generously with the black pepper, plus additional salt and/or chili powder, and the lime juice, to taste. Serve hot.