Prepare a boiling water bath and sufficient jars.
Cut the tomatoes in half and heap them in a wide, nonreactive pan with the sugar, lemon juice, ginger, chili flakes, salt, and pepper.
Stir to combine. Place the pot on the stove over high heat and bring the contents to a boil. Once you've achieved a really vigorous boil, reduce the heat to medium-high and cook, stirring regularly, until the jam reduces a great deal and begins to get thick and glossy.
As you near the end of cooking, stir constantly to ensure that the jam doesn't burn.
When you judge the jam to be done, remove the pot from the heat.
Funnel the finished jam into the prepared jars, leaving 1/2 inch headspace.
Wipe the rims, apply the lids and rings, and process in a boiling water bath canner for 15 minutes.
When the time is up, remove the jars and set them on a folded kitchen towel to cool. When the jars have cooled enough that you can comfortably handle them, check the seals. Sealed jars can be stored at room temperature for up to a year. Any unsealed jars should be refrigerated and used promptly.