1. Brush a layer of olive oil on a pizza pan or cookie sheet. In a medium saucepan over medium-high heat, combine milk, water and a large pinch of salt. Bring just about to a boil, reduce heat to medium, and add cornmeal in a steady stream, whisking all the while to prevent lumps from forming. Turn heat to low and simmer, whisking frequently, until thick, 10 or 15 minutes. If mixture becomes too thick, whisk in a bit more water; you want a consistency approaching thick oatmeal.
2. Stir 1 tablespoon oil into cooked cornmeal (polenta). Spoon it onto prepared pan, working quickly so polenta does not stiffen; spread it evenly to a thickness of about ½ inch all over. Sprinkle with salt and pepper, cover baking sheet with plastic wrap and put it in refrigerator until it is firm, an hour or more (you can refrigerate polenta overnight if you prefer).
3. Heat oven to 450 degrees F. Put polenta in oven and bake for 25 to 30 minutes, or until it begins to brown and crisp on edges. Meanwhile, put one tablespoon oil in a large skillet over medium heat. Add the mushrooms and cook, stirring occasionally, until they have released all of their moisture, about 5 minutes. Use a slotted spoon to take the mushrooms out of pan; set aside. Add spinach to skillet and sauté until it releases its water and pan becomes dry; sprinkle with salt and pepper.
4. Take polenta out of oven, sprinkle with fontina cheese, then spread spinach evenly on top of cheese and top with mushrooms, bacon and sliced tomato. Put pizza back in oven for two minutes, or until cheese begins to melt and the toppings are warmed through. Cut into slices and serve hot or at room temperature. Top with grated Parmesan cheese and crushed red pepper flakes, if desired.