Position rack at bottom of the oven; preheat to 200c/ 400f.
In a small bowl, mix butter, garlic powder, onion powder, salt, and pepper.
Place chicken in the roasting pan. Lift up chicken skin around the cavity and work your fingers under the skin over the breast and legs, easing it away from the meat.
Season chicken cavity with butter mixture, about 1 tablespoon. Stuff with lemon, onion and remaining crushed garlic. Push some of the butter mixture and 4 pieces of crushed garlic under the skin and legs. Spread it as evenly as possible. Season outside of the chicken with remaining butter mixture, salt, and pepper. Drizzle with oil.
Roast chicken, breast side up, for 1 hour and 20 minutes (or more depending on the size of the chicken). Let it rest for 10 minutes before carving. Serve with pasta, mash potatoes or rice.
Video
Notes
Add-in options: dried thyme and rosemary. Spread inside the cavity of the chicken together with the other seasonings.
Optional: Add sliced carrots, potatoes and celery around the chicken. Drizzle with oil and season with salt and pepper.