In a large, stainless steel stockpot or preserving pot over medium heat, stir together the olive oil, diced onions, minced garlic and salt. Sauté until the onions are partially translucent and have some small amounts of light golden brown around the edges, about 8 to 10 minutes.
Sprinkle the garam masala over the onions and stir well. Toast until the spice is fragrant and then stir in the ginger and minced jalapeño peppers. Stir and cook for 1 more minute.
Add the tomatoes to the pot and stir well, raising the heat to medium-high.
Continue stirring until you bring the mixture to a boil. Take care to keep scraping the bottom of the pot to prevent scorching, and drop the heat to low.
Simmer for 10 minutes, stirring well frequently.
Ladle into pint (475 ml) jars, leaving a generous 1 inch (2.5 cm) headspace at the top of the jar. Use a chopstick to release any air bubbles in the jar and adjust the level, if needed, by adding more. Moisten a paper towel with vinegar and use to wipe the rims of the jars. Fix jar lids in place and tighten them appropriately.
Process in a pressure canner according to the manufacturer’s instructions at 10 pounds of pressure for 30 minutes. Let the canner come back to atmospheric pressure naturally, then open the lid and transfer to a towel-lined rack to cool undisturbed for 24 hours. Remove any rings, wash and label the jars and store in a cool, dry place for up to 1 year.