Heat oven to 190C/170C fan/gas 5. Tip the chopped butternut squash onto a tray and drizzle over the olive oil mixed with half the tamarind paste. Toss together and roast in the oven for 45 mins, or until soft.
Tip the baby spinach into a colander set over the sink, pour over boiling water until wilted, then leave to cool. Once cool enough to handle, squeeze out the excess water, then roughly chop. Take the slices of white bread and spread one with half the butter and the other side with a very thin layer of your remaining tamarind paste. Pile the spinach and cooked squash on top of the buttered side, then add the grated mozzarella and cheddar.
Dot with a splash of hot sauce, season and add a pinch allspice, then close the sandwich. Fry the sandwich in the rest of the butter for 3-4 mins each side or until the cheese has melted and the bread is golden.