Preheat the rotisserie grill to 300F.
In a microwave-safe bowl, combine the butter, kosher salt, garlic, and herbs. Microwave the ingredients on high for about one minute or until the butter fully melts. Remove the bowl from the microwave oven. Stir the mixture and set aside for five minutes.
Return the bowl to the microwave oven and cook the mixture on high for another 30 seconds to ensure that the butter is fully liquefied. Strain the butter mixture through a fine sieve. Save the garlic and the herbs.
Spatchcock the turkey, if you want to cook it butterflied. Otherwise, skip this step.
Rub the turkey with some olive oil on top and bottom (or inside and out) and season lightly with salt, black pepper, onion powder, and garlic powder.
Using a large spoon, lift the skin above each of the turkey breasts and thighs/legs, creating wide pockets. The pockets should be closed on the bottom and the sides. Fill the kitchen injector with the strained butter and inject small amounts of butter in the breasts, doing so under the skin (not through the skin), in a diamond pattern.
Add the garlic and herbs that you saved earlier in the pockets and spread the mixture evenly.
Cook at 300F for about 1 hour and 40 minutes or so until the internal temperature in the breast reaches 160F, and the thighs/legs register 185F-190F.
Remove from the grill and let the turkey rest for 5-10 minutes before slicing and serving.