1. Cut each tomato in half and use a spoon to gently scoop out and discard the watery pulp and seeds.
2. Use a knife to finely dice the tomatoes into pieces that are about 1/16-inch thick.
3. Transfer the tomatoes to a large glass or stainless steel bowl.
4. Cut the stem end off the jalapeno, then slice the pepper in half lengthwise.
5. Use the tip of the knife to scrape out the seeds and white membranes, finely mince them, then set them aside.
6. Finely mince the flesh of the pepper and add to the tomatoes.
7. Use a knife to finely dice the onion.
8. Transfer the diced onion to a mesh strainer and rinse under cold water for about 5 seconds, then shake gently to remove excess water and add to the tomatoes.
9. Roughly chop the cilantro and add to the tomatoes.
Add the lime juice and olive oil, then use a wooden spoon or rubber spatula to gently toss the ingredients to combine.
10. Season with salt and pepper, adjusting to taste.
11. If additional heat is desired, mix in some of the reserved membranes and seeds, tasting as you go.
12. Allow the salsa to rest at room temperature for about 15 minutes.
13. The salsa should be consumed within two hours of making, after which it can become watery and oniony and lose its crunch and fresh, bright flavors.

Makes about 4 cups