Prepare the fajita seasoning by combining all ingredients in a small bowl and stirring until thoroughly blended. Store any excess in an airtight container for later use.
Prepare the cilantro-lime sauce by thoroughly combining all ingredients in a medium glass or other non-reactive bowl. Cover and place in the refrigerator until ready to use.
Heat the olive oil in a large skillet over medium-high heat. Add the bell peppers, onion, and balsamic vinegar to the skillet and season with salt and pepper, to taste. Cook for 10-12 minutes or until the onions and peppers are crisp tender.
Add the shredded rotisserie chicken, fajita seasoning, and chicken stock to the skillet and stir to combine. Cook until heated through and excess liquid is gone, approximately 3-4 minutes. Season with additional salt or fajita seasoning, if desired.
Remove skillet from heat and stir in the cilantro, green onions, and fresh lime juice. To serve, spoon mixture onto individual Romaine lettuce leaves and top with a drizzle of cilantro-lime sauce. Enjoy!