Prepare ingredients: thinly slice the 1/4 red onion and separate the 8 butter lettuce leaves; pat the shredded chicken dry with paper towels if damp. Mince the 1 chipotle pepper and the 1 garlic clove. Chop cilantro and cut the lime into wedges; reserve one wedge for finishing.

Prep: Finely slice the 1/4 red onion. Finely chop the cilantro. Cut the lime in half. If the chipotle is from a can in adobo, finely chop it (include a bit of adobo sauce if you like more heat); if it's a dried chipotle, rehydrate in hot water for 10 minutes and finely chop. Set the 8 butter lettuce leaves on a platter and pat dry.

Heat 1 tablespoon olive oil in a large skillet over medium heat. Add the sliced red onion and sauté 3–4 minutes, stirring occasionally, until softened and beginning to color.

Heat a wide skillet over medium heat and add 1 tablespoon olive oil. When the oil shimmers (about 30 seconds), add the sliced red onion and sautée for 3–4 minutes until softened and translucent.

Add the minced garlic and minced chipotle pepper to the skillet and sauté 30–45 seconds until fragrant. Stir in 1/2 teaspoon ground cumin and 1/4 teaspoon dried oregano; cook 15 seconds to bloom the spices.

Add the chopped chipotle pepper to the skillet and cook, stirring, for 30–45 seconds until fragrant. Sprinkle in 1/2 teaspoon ground cumin and 1/4 teaspoon dried oregano; stir to combine and toast the spices for 15–20 seconds.

Pour in 1 cup tomato sauce and stir to combine. Bring the sauce to a gentle simmer, reduce the heat to low, and cook 6–8 minutes uncovered, stirring occasionally, until the sauce thickens slightly and the flavors meld.

Pour in 1 cup tomato sauce and stir, scraping any browned bits from the pan. Bring the sauce to a gentle simmer, reduce heat to low, and let simmer 6–8 minutes to deepen the flavors and reduce slightly.

Add the 1 lb shredded chicken to the skillet and toss to coat evenly with the tinga sauce. Cook 3–5 minutes until the chicken is heated through and absorbs the sauce. Taste and season with 3/4 teaspoon salt and 1/4 teaspoon black pepper (adjust to your taste). If the mixture seems too thick, squeeze in 1–2 teaspoons fresh lime juice to loosen and brighten flavors.

Stir in the 1 lb shredded cooked chicken, 1/2 teaspoon of the kosher salt (from the 3/4 tsp), and 1/8 teaspoon black pepper. Increase heat to medium-low and cook, stirring occasionally, 4–5 minutes until the chicken is heated through and well coated with the sauce. Taste and adjust seasoning — add the remaining salt and pepper if needed.

Stir in 2 tablespoons chopped cilantro and the juice of half the lime (reserve remaining lime for serving). Remove skillet from heat.

Turn off the heat and squeeze the juice of 1/2 to 1 lime (start with 1/2 lime, taste, then add more if you like). Stir in 2 tablespoons chopped cilantro, reserving a little for garnish.

Assemble the lettuce cups: divide the chicken tinga evenly among the 8 butter lettuce leaves (about 2–3 tablespoons per leaf). For a plated serving, give 2 leaves per person (4 servings). Garnish with the reserved cilantro and a few thin onion slices or an extra lime wedge on the side.

Assemble the lettuce cups: place the butter lettuce leaves on a platter. Spoon about 2–3 tablespoons (roughly 2 oz) of the warm chicken tinga into each leaf. Top each cup with a few thin slices of red onion and a sprinkle of additional cilantro if you like.

Serve immediately with lime wedges on the side for squeezing. Leftover tinga stores in an airtight container in the refrigerator for up to 3 days—reheat gently in a skillet or microwave before assembling.

Serve immediately while warm. Leftovers: store the chicken tinga sauce and shredded chicken in an airtight container in the refrigerator for up to 3 days; store lettuce separately. Reheat gently on the stove over low heat (add a splash of water) or microwave in 30-second bursts.