Preheat the oven to 190°C.
Wash and pat dry the asparagus, then snap off their woody ends.
Mix the pesto with the lemon zest in a small bowl. Squeeze out the garlic flesh from their skin and mix with the pesto. Add the pine nuts if used.
Unroll the puff pastry on a flat worksurface. Using a pizza-cutter, cut out squares or rectangles - big enough to fit the asparagus, allowing a border of about 1cm. Using a kitchen knife, mark this border all around the tarts, 1cm from the edge.
Using a silicon brush glaze the tarts with the pesto mixture, up to the border, then loosely lay about 5 asparagus on top. (if the asparagus is too thick, you might want to cut them in half horizontally).
Scatter some cheese on top (if used), then bake for 15-20 mins until the pastry is golden and the asparagus is lightly charred.
Serve warm or at room temperature.