1 ½ cups water or chicken broth, plus more as needed
1 (14 ounce) bag corn tortilla chips
12 ounces shredded Cheddar cheese
12 ounces shredded Monterey Jack cheese
1 avocado - peeled, pitted and diced
½ cup chopped white onion, or to taste
2 ripe tomato, chopped, or more to taste
1 jalapeno pepper, seeded and minced
½ cup sour cream, for topping
½ cup chopped fresh cilantro
Step 1 Season both sides of steak with salt and pepper. Heat oil in a skillet over medium-high heat. Cook steak, turning occasionally, to medium doneness, about 6 minutes per side. An instant-read thermometer inserted into the center should read 135 to 140 degrees F (60 degrees C). Transfer meat to a bowl to let it rest.
Step 2 Pour a splash of water into the skillet; stir to scrape up browned bits and deglaze the pan. Pour this liquid over meat. Allow meat to cool completely.
Step 3 When meat is completely cool slice thickly (about 1/2 inch) with the grain, then cut into thinner strips. Dice by cutting into pieces against the grain. Transfer chopped steak back to the bowl; toss with the pan drippings.
Step 4 Melt bacon fat over medium heat in a pot. Add onions and a pinch of the salt; cook and stir until softened, 5 or 6 minutes. Stir in oregano. Add pinto beans and water. Bring back to a simmer and cook until onions are soft and sweet, about 5 minutes. Reduce heat to low.
Step 5 Mash the beans with a potato masher to your desired consistency. Add additional liquid, if necessary, to achieve your preferred texture. Add the remaining salt to taste. Remove from heat.
Step 6 Preheat oven to 450 degrees F (230 degrees C).
Step 7 Place tortilla chips about 2 or 3 deep in a heat proof pan. (You may need more than one pan.) Top chips with spoonfuls of beans and a generous handful of steak pieces. Sprinkle with grated cheese.
Step 8 Bake in preheated oven until cheese is melted and edges start to brown, about 10 minutes.
Step 9 Scatter diced ripe avocado, diced onions, diced tomatoes, and diced jalapenos over the top. Drizzle nachos with sour cream and garnish with chopped cilantro.