The story of French Bread Pizza dates back to 1960 when a food truck owner in Ithaca, New York (home of Cornell University) named Bob Petrillose started making and selling pizzas using French bread because he allegedly didn't like selling pizza by the slice. He called it PMP or "Poor Man's Pizza". It finally hit the mass consumer market in 1974 when Stouffer's started selling frozen pizzas in supermarkets.
Part of the allure of French Bread Pizza is being able to make it at home, letting you customize it with exactly the toppings you want on it. My dad used to make it when I was growing up, and it was always a hit in our family. I don't recall him ever making his own pizza sauce for it, choosing instead to buy it while picking up the rest of the ingredients.
I decided to go one better, and try to make my own pizza sauce using one of many different recipes posted online. What's the difference between pizza sauce and spaghetti sauce? Pizza sauce isn't cooked before it goes on the pizza - it cooks with the pizza. This one's pretty simple, and has a good basic flavor; you could change it up a bit by adding other seasonings (I found versions that use fennel, basil, and even anchovy paste - yuck!). It makes about two cups of sauce, which should be plenty for most sized loaves of French bread (and whatever you have left over makes a great dipping sauce).
More about that bread... it's the key to the entire pizza. The loaves I usually get are long and narrow (at least larger than a baguette), but some are much wider like Italian breads. This can have a big impact on how much sauce and toppings you can pile on them (for example, the as-found recipe I used called for three cups of pizza sauce, but the loaf I bought could barely hold one cup). So, you'll need to be a bit flexible with some of the measurements.
Another key item is keeping the bread from getting soggy while it bakes. This is done by "pre-baking" it with a coating of olive oil to crispen the outer edges.
Toppings can be whatever you want on your pizza - I created a "supreme" version that included Italian sausage, onions, mushrooms, pepperoni, and black olives, but you could also have peppers, ground beef, ham, bacon, or even pineapple. This is truly a "take it and make it your own" kind of dish.
Pizza adapted from Serena Bakes Simply from Scratch
Sauce adapted from Four Hats and Frugal