Heat oil in a nonstick skillet, then add garlic and 1 teaspoon of chipotle and cook for about 30 seconds. Stir in 4 tablespoons of cilantro, orange juice, and Worcestershire sauce. Add chicken, bring to a simmer, cover, and cook until the thickest part of the chicken reaches 160 to 165°F, approximately 12-18 minutes.
Transfer the cooked chicken to a plate, let it cool, and then shred it. Continue simmering the sauce until it thickens and reduces to 1/3 cup, about 2 more minutes. Off the heat, stir in mustard, 2 more tablespoons of cilantro, and the shredded chicken. Season with salt and pepper to taste.
In a separate bowl, whisk together sour cream, remaining chipotles, and remaining cilantro, then season with salt and pepper. Serve the chicken in warmed tortillas with the sour cream mixture.