Place tomatoes in a strainer or colander set over a large bowl. Toss with 1 teaspoon salt and let sit 5 minutes.
Transfer tomatoes to a large bowl. Add avocados, corn, jalapeño, onion, cilantro, lime juice, garlic, and cumin; season with remaining 1 ½ teaspoons salt and toss to combine.
Make Ahead: Salsa can be made 3 days ahead. Store in an airtight container and refrigerate.
