Prepare the Balsamic Glaze:
In a small saucepan, combine the balsamic vinegar and honey (or brown sugar). Heat over medium heat until the mixture reaches a gentle boil.
Reduce the heat and let it simmer, stirring occasionally, until the mixture reduces by about half and thickens (approximately 10 minutes).
Remove from the heat and transfer the glaze to a heat-safe bowl to cool. It should be thick enough to lightly coat the back of a spoon.

Assemble the Salad:
In a large mixing bowl, combine the baby spinach, sliced strawberries, blueberries, and crumbled feta. Toss gently to combine.
Divide the salad into individual bowls or plates. Top each with a mix of whole and chopped toasted pecans.
Drizzle the cooled balsamic glaze over each serving just before serving.