Put on the pasta water, add salt and cook the pasta.
Meanwhile, cover and defrost the spinach in the microwave, quarter the tomatoes, pour off the water from the tuna and chop up a little with a fork.
Fry the onion in a little oil in a saucepan.
When the spinach has thawed, pour the liquid that has leaked into the pan (add a little water if necessary) and melt the cream cheese in it on the lowest setting. Sprinkle with the flour.
Then add the spinach and garlic. The consistency can be very runny. Bring to the boil briefly and then fold in the pasta and tuna and bring to the boil again, stirring constantly. Finally add the tomatoes and season to taste.