Add 1 cup of hot water to a small bowl. Add the dried porcini and steep them for 15 minutes.
Heat the olive oil on medium heat in a large skillet; add the onion and zucchini (if using zucchini)and cook until the onions are translucent and soft (but not browned).
Add the rice and stir with a wooden spoon about 3 minutes. Add the white wine and cook about 1-2 minutes stirring with the wooden spoon.
Add a 4 to 6-ounce ladle of stock and cook, stirring, until it is absorbed. If using dried porcini mushrooms, strain the liquid (reserve it) it's in and chop the dried mushrooms.
If using dried porcini, add the dried porcini and the strained liquid they soaked into the rice.
Continue adding the stock a ladle at a time, waiting until the liquid is absorbed before adding more. Just before adding the last 4 to 6-ounces of stock add the freshly sliced porcini (if you're using fresh porcini). Depending on if you're stock/broth was salted, check the risotto and see if it needs some salt (add salt to taste).
Cook until the rice is tender and creamy and al dente, about 15-20 minutes. Remove the pan from the heat.
If using fresh spinach, add when the rice is al dente. Stir in the butter and cheese until well mixed.
Serve hot. Ladle out onto plates and grate on some more Parmigiano-Reggiano (if you like). ENJOY!