Bring a large pot of water to a boil. Add the salt and then cook the pasta according to the package directions. When your pasta is cooked, drain and set aside.
Meanwhile, add the olive oil, chili flakes and garlic in a large skillet and heat over medium heat. Stir the garlic and chili flakes often and after a few minutes (when your oil has heated), add the zucchini. Cook, stirring regularly until the zucchini slices start to brown.
Next add in the mushrooms. Cook for 1 - 2 minutes, stirring regularly and then add the sliced tomatoes to the pan. Cook, stirring occasionally.
When you see that your tomatoes have cooked down a little bit, add in your spinach. The liquid which has been released by the mushrooms and the tomatoes will help to cook down the spinach.
As soon as your spinach has cooked down (this will take less than a minute), add the drained pasta to the skillet. Reduce the heat to low and gently stir everything together so that the vegetables get evenly tossed with the pasta. Add salt to taste, if desired.
Serve immediately and enjoy!