Toss the pumpkin with a little oil and salt and pepper in a heavy bottom baking tray and cook in the oven until tender tossing now and again.
At the same time, put the pearl barley and a pinch of salt in a pot and just cover with stock and gently cook for about 35 minutes until just tender, adding more stock if needed and then drain well.
To make the mornay sauce, melt the butter in a pot and add the flour and stir well and gently to cook and then add the hot milk, all at once, and whisk well and then add 2 good handfuls grated tasty cheese, the cream and salt and pepper and whisk until the cheese has melted.
Heat a little oil in a pan and gently saute the tomatoes until they collapse a bit, regularly stirring and then toss the tomatoes with the cooked pumpkin, pearl barley and salt and pepper and add a general amount of the mornay sauce (LEAVE ENOUGH TO COVER THE TOP OF THE BAKED DISH) and mix well and transfer the mixture to a gratin dish (or any ovenproof dish).
Flatten the top and then spoon more mornay sauce on top and sprinkle with some grated cheddar and parmesan and cook in the oven for about 20 minutes or until golden and bubbling.
Can be made ahead and reheated in the oven though you may need to cover with alfoil to prevent cheese burning.