Bring a large pot of salted water to a boil over high heat. Add the pastina and cook for half the time recommended on the package. The pasta should still be very firm in the center as it will be cooked more.
Reserve 1 cup of the pasta water, then drain the pasta, rinse with cold water, and drain again. Drizzle with 2 tablespoons olive oil to keep the pasta from sticking together. (You can prepare the pasta to this point up to 8 hours ahead; refrigerate it until you are ready to finish the dish).
Heat 2 tablespoons olive oil in a large pot over high heat. Add the garlic and saute until browned. Add the oregano and cook briefly to release its fragrance, then add 1 1/2 cups water. Bring the liquid to a boil, add the partially cooked pasta, and stir to coat. Add 1 cup stock or broth, season with salt and pepper, and simmer until all the liquid has been absorbed, 3 to 4 minutes.
Add the Roasted Tomato and Pepper Sauce and 1/2 cup Parmesan cheese, then stir in the spinach to wilt. Thin, if desired, with some of the reserved pasta water. Remove from the heat, place in serving spoons and sprinkle with grated Parmesan. Serve warm.
Note: If you don't have any small pasta shapes in the pantry, you can grind spaghetti in your food processor until it's reduced to short lengths.
Roasted Tomato and Pepper Sauce:
Put the rack in the center of the oven and preheat the broiler to high.
Smash the tomatoes with your hands and put them and their juice to a large bowl. Add the peppers, garlic, oil, vinegar, and rosemary. Season with salt and pepper and mix the ingredients well. Pour out onto a shallow baking pan and place the pan on the middle rack of the oven under the broiler for 15 minutes. Give the mixture a good stir and cook for another 15 minutes, or until the peppers are tender.
Puree the mixture in batches in a blender. (Do not fill the blender more than half full and hold a kitchen towel firmly over the blender lid while pureeing. Hot liquids can expand causing the lid the pop off and the hot liquid to splatter.) If not using right away, allow to cool to room temperature before refrigerating.