Place the finely diced white onion in a fine-mesh strainer and rinse under cold running water for 30 seconds. Pat dry with a paper towel. This process, known as 'deflaming', removes the harsh sulfurous compounds for a cleaner flavor.

Halve the avocados, remove the pits, and scoop the flesh into a large chilled mixing bowl.

Drizzle the lime juice immediately over the avocado to prevent oxidation. Using a fork or potato masher, crush the avocado to a chunky-smooth consistency, ensuring some visible chunks remain for texture.

Add the rinsed onions, minced jalapeño, and chopped cilantro to the bowl.

Incorporate the kosher salt and ground cumin, folding the mixture gently with a spatula until the aromatics are evenly distributed.

Fold in the diced Roma tomatoes last to maintain their structural integrity and prevent the guacamole from becoming watery.

Taste for seasoning balance and add additional salt or lime juice if required. Serve immediately with corn tortilla chips.