Make the Dressing: In a small bowl or jar, whisk together olive oil, honey (or maple syrup), Dijon mustard, and lemon juice. Stir in poppy seeds and a pinch of sea salt. Taste and adjust to your liking.
Prep the Ribbons: Use a sharp vegetable peeler or mandoline to shave the cucumber and melon into thin ribbons. For melon, cut into wedges, remove the rind, and peel from the flat side. Blot gently with paper towels if overly wet.
Assemble the Salad: Layer the cucumber and melon ribbons gently in a bowl or on a platter. Drizzle with poppyseed dressing. Top with crumbled feta, torn mint leaves, and a pinch of flaky salt. Serve immediately.