Zest and juice the limes, setting aside 1 teaspoon of the zest for garnishing. Combine lime juice with thinly sliced red onion, sugar, and kosher salt; let mixture pickle for about 15 minutes.

In a separate bowl, mix lime juice, minced garlic, chopped cilantro, olive oil, remaining sugar, and salt; whisk together until smooth.

Layer torn butter lettuce leaves in a large salad bowl, followed by sliced cucumbers, halved cherry tomatoes, peach slices, and crumbled feta cheese.

Drain pickled onions and sprinkle them atop the assembled salad; add pumpkin seeds and reserved lime zest.

Drizzle half of the vinaigrette over the salad and toss gently to combine; serve immediately with remaining dressing on the side.