Heat a grill or grill pan over medium high heat.
Brush the pineapple with oil and place on the grill. Cook until grill marks form, 3-4 minutes. Flip and cook another 3-4 minutes on the second side. Remove from grill. Chop the pineapple and place it in a bowl along with the red onion, cilantro, jalapeño and lime juice. Mix to combine. Season the salsa with salt and pepper to taste.
Cut the fish into 1-inch wide strips and place them in a bowl along with the thyme, paprika, onion powder, garlic powder, cayenne pepper, ½ teaspoon salt and ¼ teaspoon black pepper. Toss to coat all of the pieces of fish evenly.
Brush the grill with oil and add the fish. Cook 3 minutes then turn the fish over and cook another 2-3 minutes until opaque. Remove the fish from the grill.
Mash the avocado and lime juice together in a bowl.
To assemble the tacos, spread some mashed avocado on the warmed tortilla. Top with a few pieces of fish and grilled pineapple salsa. Serve with additional toppings such as cilantro leaves, lime wedges and sour cream or Greek yogurt.