To make the tomatillo salsa: Preheat oven to broil. Line a baking sheet with aluminum foil.
Place the tomatillos, onion, garlic, and jalapeño (if using) on the prepared baking sheet. Drizzle with the oil and toss to coat. Broil until the vegetables are charred, 10 to 12 minutes. Transfer the vegetables to a blender. Blend until mostly smooth. Add the lime juice and cilantro to the blender and blend until smooth. Season to taste with salt and transfer to a bowl until ready to use.
To make the tacos: Place the shrimp in a large bowl. Sprinkle with the Spice Mix, garlic, 1/2 teaspoon salt, and 1/2 teaspoon pepper and toss to coat.
Melt the butter in a large heavy-bottom or cast-iron skillet over medium-high heat. Add the spiced shrimp to the skillet and cook undisturbed for 2 minutes. Flip and toss until the shrimp is opaque and fully cooked. Transfer the shrimp to a plate.
Add the tomato paste to the skillet and cook for about 30 seconds, then add the pineapple and stir to coat. Cook until the pineapple chars slightly and releases its juices, about 3 minutes.
Cook the tortillas on both sides over a low open flame until they are browned and slightly charred, 30 seconds to 1 minute per tortilla.
Add the shrimp back to the skillet and toss to coat. Remove from the heat. To assemble, place a spoonful of shrimp mixture, a dollop of salsa, and a sprinkle of cabbage on each tortilla. Enjoy!
Spice Mix
In a small bowl, combine the paprika, chili powder, oregano and cumin and mix well.