Preheat the convection oven to 200°C / 400°F.

Peel 6 garlic cloves and coarsely crush them with 1 tablespoon black peppercorns and 1 teaspoon salt.

Chop the fresh coriander, green bell pepper, and spring onions. Combine them with the crushed garlic mixture in a mixing bowl.

Stir 1 tablespoon paprika and 1 teaspoon rondelle powder into the marinade until evenly combined.

Loosen the skin of the whole chicken without cutting the flesh. Rub about two-thirds of the marinade underneath the skin.

Spread 2 tablespoons butter under and over the chicken skin. Cover the chicken with aluminum foil and let it rest for 15 minutes.

Place the chicken in a roasting pan and set a small oven-safe dish containing 1 cup water beside it. Roast covered for 45 minutes.

Peel and cut 700 g yam and 700 g sweet potatoes into large chunks. Slice the 2 onions.

Put the yam in an oven-safe baking dish with 1/4 cup water. Cover with aluminum foil and bake for 25 minutes until nearly tender.

Add the sweet potatoes and sliced onions to the yam. Pour the remaining marinade over the vegetables.

Add 1/4 cup water to the vegetable dish. Cook over high heat for 5 minutes, using an oven-safe dish placed on a stovetop only if suitable.

Brush 1 tablespoon cooking oil over the vegetables. Bake the vegetable dish uncovered for 15 to 20 minutes.

Remove the foil from the chicken and baste it with its roasting juices. Return it to the oven for 15 minutes until the skin is browned and the thickest part reaches 74°C / 165°F.

Rest the roast chicken for 10 minutes. Serve it with the roasted yam, sweet potatoes, onions, and pan juices.