Prepare the chicken for shredding: place the chicken, halved onion, smashed garlic, bay leaf, 1 teaspoon kosher salt, and enough water or low-sodium chicken broth to cover the chicken in a medium saucepan. Add 1/2 teaspoon black pepper and bring to a gentle simmer over medium heat, then reduce to low and poach until the chicken registers 165°F (74°C) and is easily pierced, about 12–18 minutes depending on thickness. Remove the chicken and reserve 1/2 cup of the cooking liquid.

Shred and season the chicken: let the chicken cool slightly then shred with two forks or a stand mixer on low for 30 seconds. Heat 2 tablespoons vegetable oil in a large skillet over medium-high heat. Add the shredded chicken, reserved cooking liquid, 1 teaspoon ground cumin, 1 teaspoon dried oregano, 1 teaspoon chili powder and cook, stirring, until most of the liquid evaporates and the spices cling to the chicken, about 4–6 minutes. Taste and add salt and pepper if needed.

Stir in the cheese: reduce heat to low and fold in 1 cup shredded cheddar or Mexican blend cheese until melted and evenly distributed. Remove from heat and let the filling cool slightly; this makes rolling easier and prevents soggy tortillas.

Warm the tortillas: to prevent tearing when rolling, warm the tortillas on a dry skillet over medium heat for 10–15 seconds per side or wrap them in a damp towel and microwave for 20–30 seconds. Keep them covered so they remain pliable.

Assemble the flautas: place a warmed tortilla on a clean work surface, spoon about 2–3 tablespoons of the chicken mixture in a line across the lower third of the tortilla, then roll tightly and place seam-side down on a baking sheet or plate. Repeat with the remaining tortillas and filling.

Crisp the flautas (oven method): preheat the oven to 425°F (220°C). Lightly brush or spray each flauta with cooking spray or a little vegetable oil. Arrange seam-side down on a rimmed baking sheet and bake 10–12 minutes, then switch to broil on high for 1–2 minutes to achieve deep golden-brown spots. Watch closely to avoid burning.

Crisp the flautas (skillet method): heat 2–3 tablespoons vegetable oil in a large skillet over medium-high heat until shimmering. Working in batches, add seam-side down and cook 2–3 minutes per side until deeply golden and crisp, turning carefully with tongs. Drain on paper towels. For a lighter finish, use 1–2 tablespoons oil and hold pan temperature slightly lower.

Quick lime crema: stir together 1/2 cup sour cream, 1 tablespoon fresh lime juice and 1/4 teaspoon garlic powder; season with salt and pepper to taste. Thin with a tablespoon of water if you prefer a drizzling consistency.

Prepare salad and garnish: toss shredded lettuce and diced tomato together and top with a sprinkle of shredded cheese if desired. For serving, arrange three flautas per plate with a mound of salad and a ramekin of lime crema; garnish with chopped cilantro and sliced jalapeño if using.

Storage and reheating: cool leftover cooked flautas to room temperature, then refrigerate in an airtight container for up to 3 days. Reheat in a 375°F (190°C) oven for 8–10 minutes until heated through and crisp, or re-crisp in a hot skillet for a few minutes per side.