1. Preheat the oven to 225°C.
2. Combine 2 tablespoons of the oil with the cumin, coriander, 2 teaspoons salt and 1 teaspoon pepper in a small bowl.
3. Rub the spiced oil all over the chicken pieces and place on a foil-lined shallow-rimmed baking sheet.
4. Roast until the chicken is golden brown and crisp and a thermometer inserted into the thickest parts registers 72°C, about 45 minutes.
5. Meanwhile, toast the pepitas in a large dry skillet over medium heat, stirring occasionally, until crisp, about 5 minutes.
6. Cool and coarsely chop. Transfer to a medium bowl, add the coriander, lime juice, chilli, onions, remaining 2 tablespoons oil and 3/4 teaspoon salt and toss together.
7. Arrange the chicken pieces on a platter and serve with the bowl of salsa on the side, accompanied by Mexican rice and black beans.