Preheat the grill over medium-high heat for 10 minutes with the lid on. Lightly oil the grill.
Meanwhile, in a small bowl, whisk together the avocado oil, brown sugar, and cinnamon. Using a pastry brush, brush the mixture on both sides of each pineapple spear.
Add the pineapple spears to the hot grill in a single layer. Cook for 2-4 minutes per side, or until golden brown and tender. If you have reserved brown sugar mixture, you can brush it on at the end.