Preheat grill to medium-high heat or set your oven broiler on high.
In a large bowl, combine the ground chicken, Panko breadcrumbs, Italian breadcrumbs, dried onion (or fresh onion), seasoned salt, garlic powder, and dry ranch dressing mix until evenly mixed; avoid overworking.
Divide the mixture into four equal portions and shape each into a patty about 3/4-inch thick.
Oil the grill grates or grease a broiler pan, then place the patties on the grill or broiler pan.
Cook the patties 4–6 minutes per side, flipping once, until the internal temperature reaches 160°F (71°C).
During the last minute of cooking, place a slice of cheddar on each patty and allow it to melt; then remove the patties from heat.
Spread the butter on the cut sides of the buns and toast them under the broiler or on the grill until golden, about 1–3 minutes.
Assemble burgers by placing each cheddar-topped chicken patty on a bun and add optional lettuce and prepared ranch dressing as desired.