Combine the brown sugar, onion powder, garlic powder, thyme, salt, ginger, allspice, cinnamon, black pepper, smoked paprika and nutmeg in a mixing bowl, then whisk in the vegetable oil.
Pour the spice blend into a large zip-top bag, and add the steak. Massage lightly to evenly coat the steak. Seal and refrigerate for 2 to 4 hours.
Once the meat has marinated, bring your grill or grill pan to high heat. Use tongs to remove the steak from the bag and place directly onto the grill. Cook for about 4 minutes, flip and repeat. Transfer the steak to a cutting board and let rest for 10 minutes.
Cut the steak into several 4”-long cross sections along the grain. Then cut each cross section into 3 to 4 strips against the grain, severing the long muscle fibers and making the steak easy to chew.
Assemble the tacos starting with a few strips of steak, followed by the pineapple salsa and sour cream.
*Pineapple salsa: Combine 1 cup diced fresh pineapple, 1 minced shallot, 1 tbsp minced jalapeño, 1/3 cup lightly packed chopped cilantro and 1 tbsp fresh lime juice.