Preheat the oven to 180 degrees Celsius.
Start by cooking the barley with the water and salt in a small saucepan over medium heat for 20 minutes.
While the barley is cooking, prepare the pumpkin and place it on a lined baking tray to cook for 15 minutes.
Remove the tray from the oven, add the cooked barley, chicken, green beans and red onion.
Drizzle over olive oil and lemon juice and season with salt and pepper.
Return tray to the oven for approximately 15-20 minutes, until the chicken is cooked through.
Remove from the oven and serve.