Place the butternut squash in a pan of water, bring to the boil, reduce to a simmer and cook for 6-8 minutes, or until tender add the peas to the pan for the last 2 minutes, drain, place in a large bowl and set aside.
In the same pan, melt a knob of butter, add the spring onion and garlic and cook for 1-2 minutes.
Squeeze any excess water from the spinach and roughly chop, add to a bowl with the squash, peas, spring onions, garlic and chick peas. Stir in the harissa paste, taste for seasoning (add more if required), add the fresh coriander and stir well.
Preheat the oven to 180°C/Fan 160°C/Gas Mark 4.
Melt the remaining butter in a small pan, work with one sheet of filo pastry at a time, (keep the rest covered with cling film and a damp tea towel). Brush the pastry with a little butter on one side and cut into 2 long strips. Place a heaped teaspoon of filling at the top of one strip of pastry; fold the corner of the pastry over the filling diagonally to form a small triangle. Continue folding down diagonally to alternate sides until you reach the bottom of the strip. Brush with a little butter and place the samosa on a lined baking tray. Repeat the process until you have used all the filling. (Any remaining pastry can be kept in the freezer for a later date).
Bake in the oven for about 20 minutes, or until the samosas are crisp and golden.