In a medium bowl, whisk together the olive oil, balsamic vinegar or lemon juice, honey, Dijon mustard, and salt and pepper. Mix until emulsified.

Thinly slice the peaches and, if using, the red onion. Toast the pecans or almonds in a skillet over medium heat until fragrant.

Lay the spinach or arugula in a large bowl, then top with the peaches, red onion, cheese, toasted nuts, and basil or mint.

Drizzle the dressing over the salad and toss gently to coat all ingredients. Serve immediately.