Marinate the chicken breasts in buttermilk for at least 30 minutes or up to overnight in the refrigerator.
In a bowl, combine flour, garlic powder, onion powder, paprika, cayenne pepper, salt, and pepper.
Remove chicken from buttermilk, letting excess drip off, then dredge in the seasoned flour mixture until fully coated.
Heat about ½ inch of cooking oil in a large skillet over medium-high heat until shimmering.
Fry the coated chicken breasts in the hot oil for 6-7 minutes per side, until golden brown and cooked through to 165°F (75°C).
Drain cooked chicken on paper towels and immediately toss in buffalo sauce to coat.
In a bowl, mix shredded cabbage, shredded carrots, and ranch dressing to make the slaw.
Toast the burger buns in the skillet until golden brown, if desired.
Assemble the sandwich by placing buffalo chicken on the bottom bun, topping with ranch slaw, then adding the top bun.
Serve immediately with optional sliced pickles for extra crunch.