Put the mushrooms in a large plastic ziplock bag and add the pineapple juice. Close the bag and refrigerate between 4-8 hours.
Remove the mushrooms from the juice and let them reach room temperature before grilling. Season cavity with spices.
Light/heat grill to medium high heat. Brush the grids with olive oil stained paper towel.
Grill the mushrooms flat side down for 5 minutes. Mushrooms should be sweating at this point. Flip and grill the other side for another 5 minutes. Transfer to plate and serve with the spinach chimichurri sauce.