Cut the squid bodies in half widthways, then in half again so that they open out into squares. Score on one side and mix with the lemon juice and some seasoning.
Cook the squid in a preheated heavy-based frying pan or griddle pan over high heat for 1 minute on each side. Stir in the oil, garlic and parsley, then remove from the heat and set aside to cool.
Spoon the squid and dressing over the potatoes, tomatoes and spring onions and serve with some lemon wedges.