The only good fast food I ever had, and I mean GOOD as opposed to better than average, decent, OK, or edible:
Tad's steak houses, New York city, midcentury.
A Kansas city strip steak*, baked potato, "Texas" toast, salad. Period. Limited menu indeed.
Long grill, stakes put down at one end, and then flipped down the grill. However you liked your steak there were several on the grill just that degree of done. "I'll take blood rare." "Cold center or warm?"
The kicker, $1.19 ~ 1958, got to $1.99 by '64. For reference nowhere else that I knew of in the city was a comparable steak offered for under $5 but you could get some lousy, tough as leather steaks for $4 & up all over town.
Decor was formica tables & booths, red bordello flocked wallpaper. At least they got the steaks right though.
*Anywhere but New York this is a New York steak.
https://untappedcities.com/2020/01/07/the-last-night-at-tads-steakhouse-nyc-institution-closes-after-60-years/#content
On Tex - Mex.
Tex - Mex is a misnomer, should be called border food. Great similarities southern TX, NM, AZ & northern Mexico. Even, although KN would howl at this, southern CA.