Make the balsamic glaze:In a small saucepan, combine the balsamic vinegar and honey (or brown sugar). Bring to a gentle boil over medium heat, then reduce to a simmer. Cook for about 10 minutes, stirring occasionally, until the mixture reduces by half and becomes syrupy. Remove from heat and let cool.

Assemble the salad:In a large bowl, combine baby spinach, sliced strawberries, blueberries, and crumbled feta cheese. Toss gently to mix.

Plate and finish:Divide the salad into individual serving bowls or arrange on a platter. Top with whole and chopped toasted pecans. Drizzle each serving with the cooled balsamic glaze just before serving.