Peel and roughly dice the tomatoes. Halve the onion and dice one half, then cut the other half in two. Dice the chorizo.
Cook the tomatoes and the two onion quarters in a saucepan over medium high heat. Add the salt and sugar. Cover and simmer until tender; about 30 minutes. Puree using an immersion blender (or in batches in a food processor).
Heat the olive oil in a large frying pan and cook the diced onion until soft. Add the diced chorizo and cook for 10 minutes. Add the tomato sauce to the frying pan and stir well.
Meanwhile, boil the macaroni in plenty of salted water until al dente; about 8 minutes.
Toss the sauce with the drained macaroni and serve straightaway.