Preheat the oven to 350°F.
Cook the pasta according to package directions until just al dente.
Meanwhile, heat the oil in a large non-stick skillet over medium heat. Add the onion and sauté until soft and translucent, about 4 to 5 minutes.
Add the tomato paste and oregano and stir well until well combined. If the mixture is too dry, add a splash of the pasta cooking water or just plain water.
Add the vegan chorizo to the skillet and break it up with a wooden spoon. Cook, stirring occasionally, until warmed through and fragrant, about 3 minutes.
Add the crushed tomatoes and stir to combine. Cook, stirring occasionally, for about 10 minutes to allow the flavors to meld.
Stir in the cooked pasta and spinach, if using.
Transfer the mixture to a 9x13 baking dish (or a 3-4 quart casserole dish). Bake for 15 to 20 minutes, until hot and bubbly.
Drizzle the vegan liquid mozzarella over the top and broil for 5 to 10 minutes until browned and gooey.
Serve hot.