How to Make It
Heat the oven to 425°. In a large nonstick frying pan, cook the bacon over moderate heat until crisp. Remove the bacon with a slotted spoon and drain on paper towels.
In a large bowl, combine the bacon, drained spinach, pepper jack, salt, and pepper and mix well. Brush the pizza shells with the oil. Divide the spinach mixture evenly between the two pizza shells and sprinkle the Parmesan over the top.
Bake the pizzas directly on the oven rack (for a crisper crust) or on two baking sheets until the cheese is melted, about 10 minutes.
If you want to use fresh spinach, remove the stems and then wash the leaves well and shred them. Cook the spinach in one tablespoon of the bacon fat over moderately high heat until just wilted, about two minutes. Squeeze out the excess liquid and then combine with the other ingredients, as in Step 2. Since fresh spinach cooks down to such a small amount, you will need about three pounds to equal the amount of frozen spinach used here. If you don't mind having less spinach on your pizza, one pound per shell is fine.