Easy Sour Cream Chicken Enchiladas

vegetable oil

skinless, boneless chicken breast, diced {I found this to be about 2 medium sized breasts}

white onion, chopped

Salt and pepper

{8 in} flour tortillas

& 1/2 cups monterey cheddar cheese, divided

butter, salted

all-purpose flour

{14.5 oz.} can chicken broth

sour cream

{4.5 oz.} can chopped green chiles