Preheat & Prep: Start by preheating your oven to 180°C (350°F). Line a large, rimmed baking sheet with parchment paper for easy cleanup.
Mix the Marinade: In a small bowl, whisk together the olive oil, minced garlic, and all the spices until you have a smooth, fragrant paste.
Coat the Ingredients: Place the chicken pieces, potato slices, and red onion wedges into a large mixing bowl. Pour the marinade over them and use your hands (or tongs) to toss everything together, ensuring every piece is well-coated in the spice mix.
Arrange the Tray: Spread the mixture onto the prepared baking sheet in a single layer. For the best results, tuck the onion wedges between the chicken and potatoes so they caramelize without burning too quickly.
Roast to Perfection: Place the tray in the center of the oven. Bake for 1.5 to 2 hours (using top and bottom heat). About halfway through, you can carefully baste the chicken with the juices from the pan.
Serve: The dish is ready when the chicken is golden-brown and crispy, and the potatoes are fork-tender.