Trim the baby gem lettuces and separate the leaves, keeping the smaller core leaves for salad. Wash and drain well. Arrange on a platter. Rinse and trim the spring onions and separate the green part from the white. Diagonally slice the green part of the spring onion and reserve for later. Finely slice the white part.
Heat a large non-stick frying pan or wok over a medium high heat. Add the pork mince and stir fry for 2-3 minutes until coloured and beginning to brown. Add the ginger, garlic, chilli, lemongrass paste, if using, and white part of the spring onion to the pan and stir fry together for a further two minutes.
Scatter over the reserved sliced spring onions, pour the fish sauce and lime juice on top and cook for 30 seconds more, stirring constantly. Remove from the heat and tip into a serving bowl. Garnish with fresh coriander. Spoon the fragrant mince mixture into the little gem leaves to serve.
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