Make a herb butter by combining the butter with the thyme, seasoning, spice and zest in a bowl. Mix well.
Place the grouse onto a rack in a roasting tin and rub all over with the herb butter. Lay the streaky bacon over the top.
Roast in the preheated oven for 1 hour to 90 minutes, until the meat around the thigh joint is no longer pink and the juices run clear. Remove form the oven and allow to rest, covered with tin foil, for 8 minutes. Remove the foil then slice and enjoy!