2 medium tomatoes, seeded and chopped in 1/3-inch pieces
½ cup red onion, finely diced
¼ teaspoon sea salt
1 lemon wedge, cut lengthwise in quarters
1 tablespoon balsamic vinegar
2½ tablespoons extra-virgin olive oil
1½ tablespoons fresh chives or Italian parsley, finely chopped
Toss the chopped tomatoes in a bowl with the red onion and the salt. Trim the ends of the lemon wedge and pick out any seeds. Lay it on one of its flat sides and slice the wedge lengthwise thinly, then crosswise. Let the slivers of lemon fall apart and slice or chop any long pieces into short bits. Scrape all the lemon into the bowl, toss with the tomatoes. Then toss with the vinegar, oil, and chopped herbs.
Spread the marinade over grilled tuna rollatini or serve as a condiment for other grilled or steamed seafood.