Empty the two cans of cannelini beans into a pot, add a 1.5 cups of water and bring it to a boil. You want the beans really soft and mushable (if that's a word haha)

Cook the fettuccine according to the packet instructions

In a frying pan, add the sliced mushrooms to some oil and allow it cook. Once done, set aside

In a bigger pan, saute the onions and mashed garlic in some oil. Once the onions have softened add the chopped spinach, season with salt and pepper and cook till the spinach has wilted

Add a cup or two of the cooked cannellini beans and start mashing it to a paste. Continue adding all the beans and mash away. Mash until it is a smooth sauce. Finally add the mushrooms, and give it all a good stir

Place the cooked pasta in a bowl, and pour the sauce all over it. Serve right away!