Rinse the beans thoroughly, then place them in a large pot with the bacon. Pour water over the top. Use enough water to cover the beans by 1 or 2 inches. Bring to a boil over medium-high heat, then reduce the heat to low and cover. Simmer for 2 to 3 hours. If the liquid seems to evaporate too quickly, add more water during the cooking process. The beans are done when they're fork tender, without much bite.
Add the chili powder, salt and pepper. Stir and taste, adjusting the seasoning as necessary. Add in other seasonings as desired.
Heat the fat in a large skillet and cook the onions until translucent. Add the beans to the skillet and mash them until they're the consistency you want. Stir and cook them until heated, then add the grated cheese. Top with the jalapenos.