As you know pizzas are countable But when you add another word like, frozen, does it remain countable?
Generally, when you add an adjective to a countable word are there any changes?
You can buy a frozen pizza from a supermarket. (countable)
If you have friends coming over for dinner then you might purchase three different types of pizzas.
So now you have three frozen pizzas to take back home and cook in the oven. (countable)
Once your friends arrive, and they are sitting at the table. You could ask:
Pizza is both countable and uncountable. If you are talking about the food then it's uncountable as in I ordered pizza for dinner. You could very well say that you ate a pizza or ordered a pizza(meaning one pizza). But when you are talking about the kind of pizza in general, it's uncountable. For example, I like oven pizza. However, you could very well say, I had an oven cooked pizza.