Begin by mincing the tomatoes, onion, jalapeño, garlic, and cilantro together in a food processor.
Transfer the mixture into a jar and add salt at about 2% of the total weight.
Squeeze in some fresh lemon juice and give it a good stir.
Cover the jar loosely and let it sit at room temperature for 3 to 5 days until it becomes bubbly and tangy.
Once fermented, refrigerate the salsa. It can be stored for months and will continue to develop more probiotics as it ages.
