To make the polenta: In a saucepan, bring the water, milk, and salt to a boil.
Add the cornmeal in a slow, steady stream while whisking.
Simmer for about 5 minutes, stirring occasionally, until the polenta is thick.
Meanwhile, prepare the topping:
Cut the tomatoes into wedges; in a saucepan on medium-low heat, cook the garlic in the oil for a minute; add the tomatoes, salt, oregano, and vinegar and simmer for about 5 minutes, just until hot.
When the polenta is thick, reduce the heat to low and stir in the cheese until melted and smooth.
Fold in the spinach, a couple of handfuls at a time, until just wilted.
Serve the polenta hot, topped with the tomatoes and more cheese if you wish.
Recipe by Moosewood Restaurant & Recipes | Ithaca, NY at https://moosewoodcooks.com/2013/02/spinach-polenta/