1. Place the Italian sausage into a glass pie plate or other baking dish and roast it in the oven at 375° F for 20-40 minutes until it is nice and brown and roasted fully. I like to use Johnsonville Sweet Italian sausage because they roast up so nice. Depending on the fat content, some sausages won't roast up as well. And this is not necessary but if you don't roast them make sure they are added to the sauce in time to cook fully through.
2. When the sausage is done, take it out of the oven and after letting it rest for a bit, slice it lengthwise and then across at about 1/2" intervals. Set the sausage pieces aside.
3. Bring a pot of water to a boil for the pasta. I like this recipe with farfalle but any pasta could be used, like fusilli or penne or rigatoni.
4. Add the olive oil, garlic, onion, pepper flakes and black pepper to a pan large enough to hold all the ingredients. This is a one pot dish so we will not be changing to another pan. The pan I am using is 9 1/2" across and 3" deep and it holds everything just fine.
5. Make sure you have all your ingredients chopped and ready to go. When the water is boiling, turn the heat to medium high under the pan with the oil, garlic and onion. Add the pasta to the boiling water and stir it several times until the water comes back to a boil. If you are not comfortable cooking the pasta and sauce at the same time, you can cook the pasta first and drain it in a colander and it will be ready for you when the sauce is done.
6. Cook the garlic and onion until the garlic is just starting to turn lightly brown. Do not burn the garlic, it will ruin the dish! This should take about 1 to 2 minutes.
7. Add the sausage and summer squash and cook for about 1 minute.
8. Add the tomatoes and break them up with your spoon and cook for 2 more minutes.
9. Add 1/2 of the greens and stir them until they wilt and have mostly mixed into the sauce.
10. Add the remaining greens and stir again as before until they have incorporated into the sauce.
11. By now the pasta should be cooked but if it is not, let it finish. When it is ready, transfer it to the sauce with a spider or slotted spoon. Or drain it in a colander and add it to the sauce.
12. Mix it all up gently and let it rest for 5-10 minutes for the pasta to absorb any remaining liquid.