Core and finely dice the Roma tomatoes, placing them in a medium-sized mixing bowl. Finely chop the white onion, jalapeño pepper (removing seeds for less heat), and fresh cilantro leaves.
Combine the main ingredients in the bowl with the diced tomatoes. Add the chopped onion, jalapeño, and cilantro.
Add the seasonings and lime juice to the bowl. Sprinkle in the kosher salt, granulated sugar, and ground cumin, then pour the fresh lime juice over the mixture.
Gently stir all ingredients together with a large spoon until everything is evenly distributed and the salt has begun to draw moisture from the tomatoes.
For best flavor, let the salsa rest for at least 15 minutes at room temperature before serving to allow the flavors to meld together. Taste and adjust seasoning with additional salt if needed.