Place tomatoes and oak leaf in jar, add pickling spice.
Mix salt into water until dissolved. I start with 1 quart. You won't know how much you need until you fill the jar. Pour over the tomatoes making sure everything is submerged. I try to wedge in the last few so that they hold everything down. Don't under fill you jar, too much room is not good, neither is it good to fill much above the shoulder.
I prefer to use a Fido jar for my ferments, you do not have to burp them. If you're using one of these, just close it up and set on the counter. If you are using a regular mason jar cover with a dish cloth, not cheesecloth, and secure with string or rubber band during fermentation. If you use a screw top you will have to remember to burp this every day or the gasses can make it explode.
Leave you jar on the counter or in a cupboard with a saucer underneath in case it spills over. Leave it to ferment until you see bubbles. Once you have bubbles watch for the activity to die down, probably 2 to 3 weeks total time from the beginning. Refrigerate and enjoy.