Preheat the oven to 180 degrees celcius
Boil the cannelloni in salted water for 4 to 5 minutes.
Make sure all the moisture is pressed out of the spinach. Mix with the ricotta and parmesan. Season with pepper and salt. Taste! You probably need more salt than you think.
Drain the cannelloni and let it cool off for a bit. In the meantime, season the tomato with the oregano, garlic, pepper and salt and divide in the ovendish.
Transfer the ricotta mixture to a piping bag and generously stuff the cannelloni.
Put the cannelloni's in the tomato sauce and divide the rest of the parmesan on top. Bake for 20 minutes.