Prepare the peaches. Rinse and dry 3 ripe peaches. Cut each peach in half, remove the pit, then slice into thin, even wedges.
Slice the cucumber. Trim the ends from 1 English cucumber. Cut it lengthwise in half, then slice into thin half-moons about 1/8 inch thick for a crisp, even bite.
Soften the onion flavor. Thinly slice 1/4 cup red onion. If you prefer a milder taste, place the slices in cold water for 5 minutes, then drain and pat dry.
Make the dressing. In a small bowl, whisk together 3 tablespoons olive oil, 1 tablespoon lemon juice, 1 tablespoon apple cider vinegar, 1 teaspoon honey, 1/2 teaspoon Dijon mustard, 1/4 teaspoon salt, and 1/4 teaspoon black pepper.
Toss the salad. In a large bowl, combine peaches, cucumbers, red onion, basil, mint, and feta. Pour the dressing over the salad and gently toss to coat. Taste and adjust salt and pepper as needed. Top with toasted almonds or pistachios, if using.