Add a drizzle of oil to a large pan over medium heat and add onion (and jalapeños if using). Fry until they begin to soften & brown, then add beef. Break up with a wooden spoon and continue frying until nicely browned and fully cooked through.
Add in taco seasoning then stir in 1 heaped tbsp tomato puree. Fry for a few mins, then pour in 1cup/250ml beef stock and 1 can of chopped tomatoes. Deglaze the pan as necessary, give it all a good stir and allow to simmer on low-medium for 10-15mins until the sauce begins to thicken and the tomatoes have burst.
Meanwhile pop 10.5oz/300g pasta in salted boiling water and cook until JUST al dente (if it's properly cooked it'll turn soft and sloppy in the oven, you want it still a little hard). Just before draining scoop out a cup of the starchy pasta water. Pre heat oven to 200C/390F.
Combine pasta and beef with 1/3cup of starchy pasta water. Give it a good stir until everything is blended. The starchy water will help create a sauce, with the starch molecules emulsifying with the fat in the sauce. Stir in your cheese until nice and gooey, the pour into a casserole dish.
Top with crushed tortilla chips or hard taco shells (just enough to create a thin layer over the top fully covering the pasta). Spray with oil, then pop in the oven for 20mins, or until the top goes nice and golden. Be vigilant, top goes golden to burnt quickly.
Top with your favourite taco toppings (suggestions in ingredients list) and enjoy!