Heat the olive oil in a large 12-inch high-sided skillet over medium-high heat.
Add the chicken pieces, sliced yellow onion, and sliced red, yellow, and green bell peppers to the skillet.
Sprinkle the fajita seasoning and kosher salt over the chicken and vegetables and stir to combine.
Sauté until the peppers begin to soften and the chicken starts to brown, about 4–6 minutes; the chicken does not need to be fully cooked yet.
Add the minced garlic and cook, stirring, for about 30 seconds until fragrant.
Pour in the chicken stock and the can of fire-roasted diced tomatoes with their juices and stir to combine.
Add the dried pasta, bring the mixture to a boil, then reduce heat to medium to maintain a gentle simmer.
Simmer, stirring occasionally, for about 10 minutes or until the pasta is fully cooked; if the liquid reduces too much before the pasta is done, add a little more chicken stock as needed.
When the pasta is cooked and the sauce is creamy but thick, stir in the cream cheese and minced cilantro until combined.
Sprinkle the shredded Mexican blend cheese over the top and allow the residual heat to melt it, or place the skillet under a broiler briefly if using an oven-safe dish to brown the cheese.
