Heat a small, non-stick skillet to medium heat, add the butter, the pine nuts, and drizzle in 1 teaspoon of the agave nectar. Cook, stirring frequently, until the pine nuts are a medium to dark golden brown. Transfer from the pan to a plate to cool.
Prepare the dressing by whisking all the ingredients in a measuring cup. Set the dressing aside.
In a large bowl with a wide base (12-13 inches), spread the spring mix.
Next add the strawberries and onion slices, breaking them all apart and spacing them evenly.
Top with the cooled pine nuts and the feta crumbles, layering them in until they have all been used.
Whisk the dressing one more time. Using the spout in the measuring cup, drizzle long streams of the balsamic dressing in crisscross patterns across the top of the salad.
You can toss the salad if you wish. The presentation is much more attractive and dramatic if the salad is not tossed.