Peel the red onion and finely chop. Peel and crush or finely chop the garlic cloves. Pick the rosemary leaves and finely chop. Strip the chard leaves away from the stalks. Finely slice the stalks, and roughly shred the leaves.
Pour 1 tbsp oil into a pan and bring to a medium heat. Slide in the onion, garlic, rosemary and chard stalks. Sprinkle in a pinch of salt and pepper and fry for 10 mins, stirring occasionally, till soft.
Pour in 750ml boiling water and crumble in the stock cube. Scatter in the gnocchetti and stir well to combine. Bring to the boil, then reduce to a simmer and cook for 5 mins.
After 5 mins, tumble in the shredded chard leaves and stir well. Simmer for a further 5 mins, or till the pasta is cooked.
Grate the lemon zest and stir in along with half of the juice. Have a taste of the broth and add more salt and pepper if needed.
Ladle the soup into deep bowls and serve.