Turn on oven broiler 500°
Place the flour, salt and water in a standing mixing bowl and slowly begin stirring until combined. Mix until dough forms a rough ball.
Place the dough on a clean spot on your kitchen counter. Cut the dough into 4 small balls — this is easiest if you cut the ball in half, then in half again.
On a lightly-floured surface, use your hand to flatten each ball into a 3-inch patty. Use a rolling pin to roll each patty into a 6- to 8-inch circle. The pizza crust shapes can be irregular, but the dough should be so thin. (It's good to turn the dough a few times as you roll to prevent sticking, but you don't need to worry about it too much as the dough is easy to peel of the counter.)
Put a few pieces of the rolled-out dough on a 13 x 18-inch baking sheet. Prick the dough all over with a fork (this keeps it from puffing up too much).
Top matzah dough with marinara sauce and other desired pizza toppings.
Bake on broil for 5 to 7 minutes, keeping a very close eye on them, until they are golden and puffed in spots. Repeat with all the pizzas and let cool completely.