Preheat the air fryer.
Combine the lemon pepper seasoning, rosemary and pink salt in one bowl and mix.
Place the melted butter in one bowl and the olive oil in another bowl.
Divide the lemon juice equally between both bowls.
Divide the dry seasoning into equal parts in the bowl with the melted butter and bowl with the olive oil and mix.
Place the cleaned chicken on a large flat surface like a chopping board or large plate works too, as it is easier to season the meat.
Use a large spoon (upside down) to open up underneath the skin.
Place the lemon, rosemary sprigs and onion inside the cavity of the chicken.
Use some twine to tie together the legs together (downwards).
Use a pastry brush to spread the melted butter mix underneath the skin (you can tilt the chicken vertically to pour in excess butter mixture into the open pockets.
Generously coat the outside of the entire chicken with the olive oil mix.
Carefully transfer the chicken (breast side down) into the basket.
Turn the dial to "roast" , select, 180C/356F for 60 minutes, "megazone" .
Roast the chicken for 45 minutes then turn the chicken over (breast side up) and continue for a further 15 minutes (until the internal temperature of the chicken is 165F/74C) and the juices run clear, use a thermometer, if needed to check this).
Once cooked, you can collect the drippings from underneath the basket and reserve to baste the chicken.
Serve accordingly.