Preheat the oven to 375°F.
Prepare a 9x13-inch baking pan with nonstick cooking spray or a light coating of butter.
In a sauté pan over medium-high heat, melt 2 tbsp butter.
Add the cubed chicken breast to the pan.
Season with kosher salt and freshly cracked black pepper.
Cook the chicken for 2 to 3 minutes, or until lightly golden on two sides.
Transfer the chicken to the prepared baking pan.
Add the remaining butter to the same sauté pan.
Add the sliced onion, red bell pepper, and green bell pepper.
Cook for 5 to 6 minutes, or until the onions are translucent and the peppers have softened.
In a liquid measuring cup, whisk together the chicken stock and taco seasoning until fully combined.
Turn off the heat.
Transfer the cooked peppers and onions to the baking pan with the chicken.
Sprinkle the minute rice evenly into the baking pan.
Pour the seasoned chicken stock over the rice.
Add the salsa.
Stir gently until the chicken, vegetables, rice, stock, and salsa are evenly combined.
Cover the baking pan tightly with aluminum foil.
Bake on the middle oven rack for 45 minutes, or until the rice is tender and the chicken is fully cooked.
While the casserole bakes, prepare the queso.
In a medium pot over medium heat, combine the evaporated milk, Mexican cheese blend, American cheese slices, and diced green chiles.
Cook for 10 to 12 minutes, stirring occasionally, until the cheeses are fully melted and the queso is smooth.
Reduce the heat to low and keep the queso warm until ready to serve.
Carefully remove the casserole from the oven.
Remove the aluminum foil, being cautious of the steam.
Lightly fluff the rice with a fork.
Sprinkle the chopped fresh cilantro over the casserole.
Pour the warm queso over the casserole, or serve it on the side.
Serve warm.