Preheat oven to 220C/200C fan-forced. Line a baking tray with baking paper. Place chicken, half the oil and 1 1/2 tablespoons spice mix in a bowl. Toss to coat.
Place onion and capsicum on prepared tray. Drizzle with remaining oil and sprinkle with remaining spice mix. Toss to coat. Top with chicken. Bake for 20 to 25 minutes or until chicken is cooked through.
Meanwhile, mash avocado and lime juice in a bowl. Season with salt and pepper. Sprinkle chicken and vegetables with coriander and chilli. Serve with tortillas, guacamole, sour cream and lime wedges.