Heat the olive oil in a large cast-iron or non-stick skillet over medium-high heat. Toss in the bell peppers, onion, and balsamic vinegar with salt and pepper, to taste. Cook for about 10-12 minutes or until the onions and peppers are just slightly tender.
Next, add in the shredded chicken, fajita seasoning and chicken stock. Once the mixture is heated through and you can no longer see any liquid, finish with a little extra seasoning.
Remove the pan from the heat and stir in the cilantro, green onions and freshly squeezed lime juice.
Tip: If the limes are really firm, microwave it for 15 seconds to get the juice flowing before squeezing!
When you are ready to serve, spoon the mixture onto the romaine leaves and drizzle with the cilantro-lime sauce.