In a large pot, cook the pasta until al dente in salted water according to the instructions on the package.
While the pasta is cooking, in a food processor, pulse the sun-dried tomatoes with 2 tablespoons of its oil (you might need more depending on which type you get) until finely chopped.
Heat a large pan and add a tablespoon of olive oil. Add the white onion, garlic cloves, oregano and chili flakes. Let cook for a few minutes.
Once the pasta is cooked, drain it but set aside about half a cup of the pasta water.
Add the pasta to the pan with the sun-dried tomato mixture, add the spinach and the pasta water. Mix well together and let cook until the spinach has wilted.
Before serving the pasta add the grana padano cheese and mix well. Taste it and if needed add some salt.
Serve immediately, with some toasted breadcrumbs on top and freshly grated grana padano.