Rinse the asparagus in water and break off fibrous ends.
Then mix the remaining ingredients to make the marinade, using half the agave nectar and adding more (if desired) after whisking and tasting.
Pour the marinade over the asparagus spears and let sit at room temperature for 20-30 minute.
Pre-heat an outdoor grill to 400°F.
Then, place a vegetable grill pan on the grill slats and turn the heat down to medium.
Lay the asparagus spears on the grill pan in a single layer and reserve the marinade dish and leftover marinade.
Close the lid on the grill and cook for 3-4 minutes (making sure the temperature stays about 300°F).
Open the lid and flip the spears over to sear the other side. They should be nicely caramelized on the cooked side. Close the lid and cook for another 3-4 minutes.
Finally, transfer the grilled asparagus back into the marinade dish.
Transfer to re-coat in the marinade or transfer to a serving dish and pour remaining marinade over the grilled asparagus.