Preheat the oven to 200°C (fan 180°C). Place onions and 1 tbsp olive oil in a roasting tray, season, and roast for 10 minutes.
Meanwhile, fry the chicken (skin-side down) for 4-5 minutes until golden. Season with paprika, chili flakes, salt, and pepper.
Add spring onions and asparagus to the roasting tray and mix. Place chicken on top, skin-side up.
Cut avocados into quarters (leave skin on) and place them with lemon quarters around the chicken. Drizzle with remaining olive oil and season.
Roast for 20 minutes until chicken is cooked. Drizzle with balsamic vinegar before serving.