Preheat your oven to 425°F (220°C).
Pat the whole chicken dry with paper towels. In a small bowl, combine the olive oil, lemon zest, 1 tablespoon of chopped thyme leaves, garlic powder, salt, and black pepper.
Rub the herb and oil mixture evenly over the entire chicken and gently under the skin of the breast. Stuff the chicken cavity with the halved lemon and the remaining thyme sprigs.
Place the chicken breast-side up in a large roasting pan and roast for 20 minutes.
Reduce the oven temperature to 350°F (175°C) and roast for another 20 minutes.
In a separate bowl, toss the halved plums and shallots with a light drizzle of olive oil. Arrange them around the chicken in the roasting pan, then pour the chicken stock into the bottom of the pan.
Continue roasting for 25-30 minutes, or until a meat thermometer inserted into the thickest part of the thigh registers 165°F (74°C).
Transfer the chicken and plums to a cutting board to rest for 10-15 minutes. Pour the remaining pan juices into a small saucepan, whisk in the honey, and simmer for 5 minutes until it reduces into a savory sauce. Serve the carved chicken alongside the roasted plums and sauce.