Heat some olive oil in a pan and sweat the onion briefly. Add the finely diced vegetables and fry briefly. Press or finely chop the garlic and add to the pan while stirring.
In the meantime, add water and cook the pasta according to the instructions on the packet until al dente. When the vegetables are a bit seared, pour the tomato sauce on top and season with salt, pepper and oregano to taste. Briefly add the cooked noodles to the pan and stir into the sauce.