- Small-dice the fish and place in a nonreactive bowl (glass, ceramic or stainless steel) with the lime juice, jalapeno pepper, tomato, salt and pepper, and allow to briefly marinate in the fridge while you pre- pare the dressing for the salsa. Set the bowl over ice while you prepare the salsa.
- In a bowl, whisk together the minced mint with the grapefruit juice, oil, cumin, garlic and cilantro. Add the peaches and strawberries and toss. Set aside.
- To serve, use a slotted spoon to scoop salsa into martini glasses. Drain the fish and scoop over the salsa. Garnish with the onion if using.
- Serve chilled, keeping refrigerated in a bowl set over ice until the minute you are ready to use it. Store leftovers in the fridge for up to 24 hours, after draining off excess liquid.
Note: If you make the salsa a day ahead, it will taste a lot better but the fish will toughen the longer it sits in the acidic mixture, so you should plan to serve it within one to two hours of making it.