Cook Fettucine according to package directions, making sure to salt the water well. When the pasta is done cooking, reserve about a cup of the pasta water.
In a large skillet, heat the olive oil, then add the sausage, breaking it up into large chunks.
Toss the cubed chicken in the flour and about 1 ½ teaspoons of salt. Add it to the skillet once the sausage has started to brown.
When the chicken and sausage have browned, use a slotted spoon to remove them from the skillet.
To the hot skillet, add the onion, cooking until it starts to turn transparent. Add the bell peppers, mushrooms, and garlic. Cook for about 1 minute.
Making sure the skillet is at medium-high heat, add the wine while scraping the bottom of the pan. Once the wine has bubbled up and cooked for a couple of minutes, add the chicken stock.
Add the meat back to the pan, including any juices. Cook until the sauce starts to thicken slightly. Taste to check for seasoning.
Add the pasta, spinach, and about ½ cup of the pasta water into the pan and toss with the other ingredients. If the pan seems a little dry, add a little more pasta water. You don’t want it to be soupy, but you also want to make sure there is some liquid in the pan.
Remove from heat and serve into bowls. Top with the shredded mozzarella and a little parmesan. If you want to, place the bowls under the oven broiler to melt the cheese (optional).