While the peppers are steaming, heat a 12-inch skillet over medium heat, then add 2 tablespoons olive oil. Add the onion and 1/2 teaspoon of the salt; cook until the onion is nicely browned at the edges, 8 to 10 minutes. Add the tomato paste, garlic, and chili powder, and cook until fragrant, 1 to 2 minutes. Then add the beans, 1 cup of water, and the remaining 1/2 teaspoon salt, and mash with a potato masher or the back of a large fork until about half of the beans are mashed and the liquid has been absorbed, about 7 minutes.