Preheat the oven to 220C, fan-forced. Bring a medium saucepan of salted water to the boil for the pasta. Finely chop the onion. Finely chop 1 tomato. Quarter the chorizo lengthwise, then thinly slice.
Step 2 — Cook pasta
Cook the pasta in the pan of boiling water for 9 mins or until almost al dente (the pasta won't be fully cooked, but will finish cooking in the oven). Drain.
Step 3 — Start sauce
While the pasta is cooking, put the chorizo in a cold medium deep frypan over medium-high heat and cook, stirring, for 4-5 mins until golden. Remove with a slotted spoon, leaving the flavoured oil in the pan. Heat 2 tsp olive oil in the pan over medium heat. Cook the onion and chopped tomato, stirring, for 3-4 mins until softened.
Step 4 — Finish sauce
Add the Tex-Mex seasoning, chipotle (if you prefer less heat, reduce the chipotle to taste) and 3 tsp flour to the onion mixture and cook, stirring, for 2 mins. Gradually add 160ml (⅔ cup) milk and 60ml (¼ cup) water, stirring constantly to prevent lumps forming. Bring to a simmer and cook, stirring, for 2 mins or until thickened.
Step 5 — Bake pasta
Add the pasta, chorizo and one-quarter of the cheese to the sauce and stir to combine. Taste, then season with salt and pepper. Transfer to a 1.5L (6 cup) baking dish. Scatter over the remaining cheese. Bake for 10 mins or until golden.
Step 6 — Toss salad and serve
Meanwhile, combine 2 tsp extra virgin olive oil and 2 tsp white wine vinegar in a large bowl and season with salt and pepper. Coarsely chop the remaining tomato. Add the salad leaves and tomato to the dressing and toss to combine. Serve the pasta bake and salad at the table.