Heat oil in a wide skillet, pan or Dutch oven over medium heat. Add onion and garlic, saute 3 minutes or until they start to brown.
Add tomatoes, chicken broth, oregano and spaghetti. Press the spaghetti with a spatula to submerge the pasta in the liquid.
If your skillet, pan or Dutch oven is not wide enough, you might break the spaghetti into halves before cooking. Cover with the lid and reduce heat to medium-low. Cook for 8 minutes or until the pasta is al dente.
If the pasta is not cooked after 8 minutes, add a little bit more chicken broth, cover the lid and cook for another 1 to 2 minutes.
Uncover the lid and add salt. Add the spinach, stirring until the leaves wilt. Turn off the heat and top the pasta with Parmesan cheese.