I am sure somebody somewhere in south-east Asia has eaten this, and I couldn't face not using the name, but the curry paste is clearly the only Thai thing about it.
Take a fairly small, deep pie dish (mine is 6cm deep and 16cm across at the top); line it with 2/3 of the shortcrust pastry rolled fairly thick. Chop the chicken breasts into medium-sized pieces, cook in hot oil until just browning on the outside and put into the pie case. Take the seeds out of the red pepper and discard; cut the rest into medium-sized pieces. Also chop the leek into fairly small pieces.
In a saucepan, heat up a tablespoon or so of Thai Green Curry mix with about 150ml of coconut cream, until it bubbles, and cook the red pepper in the mix for about five minutes; separately, in the frying pan you used for the chicken, fry the leek until fairly thoroughly fried. Put the frying-pan's contents into the pie case; pour over the contents of the saucepan - if it still looks dry, heat up a bit more coconut cream with a bit more green curry mix and add. Fill any spare space in the pie case with bits of roast vegetable; roll out the rest of the pastry and put it on top. Pinch round the edge, because that's half the fun of pie-making.
Bake gas mark six for about 45 minutes, until the shortcrust pastry has gone golden brown. Eat hot. A pie without spare space in is delightful after the commercial kind which are full of air, and the spiced coconut cream soaks marvellously into the pastry.