Prep the Components: Carefully separate, wash, and pat dry the lettuce leaves; set them aside. Finely dice the yellow onion and red bell pepper. In a small bowl, combine the cumin, ancho chili powder, smoked paprika, granulated garlic, Mexican oregano, and optional cayenne.
Build the Flavor Base: Heat the olive oil in the Dutch oven over medium heat. Add the diced onion and bell pepper, sautéing for 4–5 minutes until they begin to soften. Stir in the tomato paste and the prepared spice blend, and cook for another 60 seconds until fragrant.
Brown the Turkey: Add the ground turkey to the pot. Use a spatula to break the meat into small crumbles as it cooks. Continue cooking until the turkey is browned all over and no longer pink, about 6–8 minutes.
Simmer and Reduce: Pour in the low-sodium chicken broth, stirring to combine everything and scrape up any flavorful bits from the bottom of the pot. Bring the mixture to a gentle bubble.
Thicken the Filling: Reduce the heat to medium-low to maintain a steady, slow bubble. Allow the filling to cook, uncovered, for 20-25 minutes. The mixture is ready when the sauce has reduced and thickened enough to cling to the meat.
Assemble and Serve: Spoon the warm turkey filling generously into the center of each prepared lettuce leaf. Garnish with fresh cilantro and offer lime wedges on the side for squeezing over the top just before eating.