Preheat the oven to 400 degrees F (200 degrees C). Line a baking sheet with foil.
Roll the lemon and cut in half lengthwise. Slice one half into quarters and set the other half aside for baking and basting. Cut onion into 4 pieces; slice one piece and sprinkle on the prepared baking sheet. Set remaining onion pieces aside.
Mix garlic salt, sage, turmeric, basil, rosemary, and pepper together until well combined; divide evenly into 2 bowls.
Rinse chicken in cold water and dry off. Trim and discard excess fat and separate skin from meat. Stuff inside of the chicken with arugula, 4 lemon slices, 3 onion pieces, and garlic cloves. Tie the legs together with twine. Spread 2 tablespoons ghee underneath the skin and another 2 tablespoons ghee on top of the skin, all over the chicken.
Add 2 tablespoon ghee and butter to one bowl of spices. Microwave for 45 seconds. Stir and spread underneath the skin. Microwave remaining 1 tablespoon ghee and brush on top of skin. Sprinkle remaining seasoning all over chicken and pat into the skin; do not rub. Lightly squeeze some of the remaining lemon half on top of chicken and place chicken, breast-side up, on the onion slices on the baking sheet.
Bake in the preheated oven until no longer pink at the bone and the juices run clear, about 1 hour and 30 minutes, basting with juices and remaining lemon juice every 30 minutes. An instant-read thermometer inserted into the thickest part of the thigh, near the bone, should read 165 degrees F (74 degrees C). Remove from the oven and let rest for 10 minutes before slicing, continuing to baste.