1. Peel and dice the onion, and saute it slightly in olive oil.
2. Wash and cut the mushrooms in thick slices and add it to the pan.
3. Cut and add the pineapple.
4. Boil and peel the tomatoes and add them when the mushrooms are cooked. Add salt and pepper if you like.
5. Leave it all to simmer until most of the vegetables water is gone.
6. In another pan boil water with salt (no oil or the sauce won't stick to the pasta) and cook the tagliatelle until al dente.
7. Drain the pasta and add the sauce on top.
8. Add the washed and drained rockets in top of sauce.