In a large cast-iron or nonstick skillet, heat oil over medium heat. Add onions and cook, stirring, until soft and lightly browned, 5 to 10 minutes. Add garlic, chili powder, chipotle peppers, cumin and oregano; cook, stirring, for 1 minute. Add tomatoes, green and red peppers and zucchini; season with salt and pepper. Bring to a boil over high heat; then reduce heat to low and simmer, partially covered, stirring often, until the juices have evaporated and vegetables are tender, about 20 minutes. Add beans and simmer, covered, for 10 minutes, stirring often; add water if necessary. Taste and adjust seasonings. Serve in individual bowls, garnished with a dollop of sour cream or yogurt and a sprinkling of cilantro.