Prepare the jalapeño ranch dressing and set in the fridge until ready to use.
Heat the grill to medium heat.
Season the chicken breasts with salt and pepper, then drizzle with just a little bit of olive oil. Grill until fully cooked, about 3 to 5 minutes per side. Just before removing from the grill place a slice of cheese on each chicken breast.
Spread the jalapeño ranch on the bottom bun, followed by lettuce, tomato, onion (if desired), then place the chicken on top, followed by extra jalapeño slices, then the top bun. Enjoy!