Start by marinating the pork. In a small bowl, mix together olive oil, minced garlic, rosemary, thyme, salt, and pepper. Rub this mixture evenly over the pork tenderloins, then cover and refrigerate for at least an hour, or preferably overnight, to allow the flavors to meld. While the pork is marinating, prepare the peach gastrique. In a medium saucepan, combine sugar, white wine vinegar, and water, bringing it to a simmer over medium heat while stirring occasionally until the sugar dissolves. Add the diced peaches and continue to simmer for about 10-15 minutes until the peaches are soft and the mixture has thickened slightly. Stir in the lemon juice, butter, salt, and pepper, adjusting seasoning to taste. Remove from heat, let the gastrique cool slightly, then blend until smooth. Return the blended mixture to the saucepan and keep warm over low heat.

When ready to cook, preheat the grill to medium-high heat. Take the pork tenderloins out of the marinade and let them come to room temperature for about 15 minutes. Grill the pork, turning occasionally, until the internal temperature reaches 145°F (63°C), which should take about 15-20 minutes. Remove the pork from the grill and let it rest for 5-10 minutes before slicing. Slice the pork tenderloin into medallions and arrange them on a serving platter. Drizzle the peach gastrique generously over the pork, and garnish with fresh herbs like thyme or rosemary if desired. This dish pairs well with roasted vegetables, a light arugula salad, and a glass of crisp white wine or a light red like Pinot Noir.