Cook the rigatoni in a large pot of boiling salted water according to the package directions; set aside.
In a large, ovenproof skillet or medium saucepan, sauté the bacon or sausage (squeezed out of its casing) over medium-high heat until cooked through; add the onion, mushrooms and garlic and cook for 5 minutes, or until soft.
Reduce the heat to medium low, add the cream stock and thyme and bring to a simmer, then add the cheese and stir until smoothly blended into sauce. Add the spinach and cook, stirring, until the greens wilt.
Add the cooked pasta noodles and stir to coat. If you're using a pot, transfer to an ovenproof baking dish, otherwise leave it in the skillet. Toss the breadcrumbs with the Parmesan and oil, or pulse torn bread and Parmesan with the oil in a food processor until well blended. Sprinkle over the pasta and broil for 2 minutes, until golden.