Add squash and onion to an oven proof dish alongside olive oil, salt & pepper and roast in the oven at 190C for about 20 minutes. Add the pine nuts and pumpkin seeds to the oven for the last 3 minutes of the roasting process.
Combine all ingredients for the filling in a large bowl, add in the squash and onions and set aside to cool down completely (important!)
Unroll a puff pastry sheet and place your filling onto the sheet in log shape. Place the second, unrolled pastry sheet on the top and gently press it onto the filling. Take a pizza cutter or a knife to carefully cut out your Wellington, leaving about 1-2 cm on the outer edges. Use a fork or your fingers to pinch the edges together. With the leftover pastry, create any decorations for the top of your Wellington.
Brush the log with a little almond milk, then place in the oven at 180C for 20-25 minutes or until your pastry is golden.
Remove from the oven, slice and serve with vegan gravy, roast potatoes & Co.