For the marinade combine the coconut oil, garlic, ginger, fresh cilantro, and lime zest and juice, mix and pour into a large zip-lock bag with the tuna steak.
Marinade in the fridge for around 2 hours.
After 2 hours remove the marinade and scrape off excess marinade (keep the rest of the marinade) grill the tuna steaks for around 4 minutes per side.
While grilling the tuna add the spinach to an oiled hot skillet and cook until wilted, then remove from the skillet.
Using the same skillet add the leftover marinade and heat until it thickens then take off the heat.
Plate the spinach, topped with the tuna steak and sliced avocado then drizzle the thickened marinade to finish.