Prepare the candied pecans: In a small non-stick skillet over medium heat, melt the butter. Add the pecan halves, brown sugar, and salt. Stir continuously for about 5-7 minutes until the sugar is melted and coats the nuts evenly. Immediately transfer the coated pecans to a piece of parchment paper and spread them out to cool completely. Once cool, gently break them apart.

Prepare the dressing: In a small jar with a tight-fitting lid, combine the olive oil, apple cider vinegar, granulated sugar, poppy seeds, and Dijon mustard.

Seal the jar and shake vigorously until the dressing is well emulsified. Taste and adjust sweetness or tanginess if necessary. Set aside.

Assemble the salad base: In a large mixing bowl, gently combine the mixed greens, sliced strawberries, and thinly sliced red onion.

Dress the salad lightly: Pour about half of the prepared poppy seed dressing over the greens mixture and toss very gently to coat, ensuring the strawberries do not break apart.

Plate and garnish: Divide the salad among four serving plates. Sprinkle each serving evenly with the crumbled feta cheese and the cooled candied pecans for crunch. Serve immediately with any remaining dressing on the side.