In a large skillet, sweat the onion, jalapeno and garlic in oil for about 8 minutes. Add the cumin and cook another 2 minutes. Add the meat and cook, breaking it up with a wooden spoon, until it is no longer pink. Add the tomato paste, chilli powder and water. Season with salt and pepper and continue cooking until almost all the liquid has evaporated. Transfer to the middle of a large serving platter.
Arrange the shredded lettuce around the meat mixture, top with diced tomatoes and cucumber and sprinkle with cheddar.
Serve with the tortilla chips and sauce.