In a small bowl, combine the paprika, cumin, garlic powder, and 1 teaspoon of brown sugar.
Slice or shred the leftover turkey meat and place it in a medium-sized mixing bowl. Add the fresh squeezed orange juice along with your prepared seasoning mixture. Mix until well combined.
Heat 1 tablespoon of olive oil in a large pot over medium-low heat. Add the seasoned turkey mixture along with the sliced onion. Cover and let it simmer for about 30 minutes, stirring occasionally.
In a large cast iron skillet, heat the remaining 2 tablespoons of olive oil on medium-high heat. Add your turkey and onions from the pot and sprinkle with the remaining teaspoon of brown sugar. Cook until browned and crispy, approximately 12 to 15 minutes.
Divide the flavorful turkey carnitas evenly between warm flour tortillas. Top with finely diced red onion, fresh cilantro, and crumbled cotija cheese.