01 - Bring a large pot of salted water to a boil. Add jumbo shells and cook just until al dente, according to package instructions. Drain well and arrange shells on a baking sheet to prevent sticking.
02 - In a large skillet over medium heat, sauté the chopped onion in a small amount of oil until translucent. Add the ground beef and taco seasoning, and cook, stirring, until the beef is browned. Stir in the black beans and tomato sauce. Simmer mixture for 5 minutes, allowing flavors to meld.
03 - In a medium saucepan over medium heat, melt butter. Whisk in flour and cook for 1 minute, stirring constantly. Gradually add milk, whisking until the mixture is smooth and begins to thicken. Stir in shredded cheese, smoked paprika, and salt. Continue mixing until the cheese is fully melted and sauce is creamy.
04 - Preheat oven to 350°F. Fill each pasta shell with a generous spoonful of the beef and bean filling. Arrange stuffed shells in a single layer in a baking dish. Evenly pour prepared nacho cheese sauce over the filled shells.
05 - Cover the baking dish with foil and bake in the preheated oven for 20 minutes. Remove foil, sprinkle a handful of crushed Doritos on top, and return to the oven for 5 more minutes, until the topping is golden and crisp.
06 - Garnish the shells with chopped cilantro and sliced jalapeños as desired. Serve immediately for best texture.