If using fresh corn, husk ears and remove silk; grill or boil until tender; cool and cut kernels from the cob.
For a smoky note, char corn on a hot grill or skillet until lightly browned.
If using frozen corn, thaw completely and pat dry to avoid watering down the salsa.
Place corn in a large mixing bowl and add diced tomatoes.
Add finely diced red onion and minced jalapeño (if using) to the bowl.
Chop cilantro and add it to the mixture for fresh herb flavor.
In a small bowl whisk lime juice, olive oil, cumin, sugar (optional), salt, and pepper.
Pour the dressing over the corn mixture and toss gently to combine evenly.
Taste and adjust seasoning with more lime, salt, or jalapeño for heat.
Let salsa rest 10–15 minutes at room temperature to meld flavors before serving; garnish with extra cilantro or a lime wedge.