Thinly slice the onion, celery and one garlic. Peel the sweet potato and carrot, then chop them into 2cm pieces.
Heat 1 tbsp of vegetable oil and gently sauté the onion, celery and garlic for 5 minutes. Add the sweet potato and carrot pieces (and chilli flakes, if used) and cook for another 5 minutes.
Pour in the stock and bring to the boil. Simmer for 5 minutes, then add the spring greens. After 5 minutes add the peas and cook for another 5 minutes.
Meanwhile cook the noodles in another pan following the packet's instructions (it should take 5 minutes or so), then drain and keep warm.
Chop the parsley/coriander leaves and mince the other garlic clove. Mix these together with the lime/lemon juice.
When all the vegetables are tender, turn off the heat and add the garlic/herb mixture and the noodles.
Serve immediately.