Preheat the oven to 200C/ gas mark 6.
Cut the sweet potato into rough 4 cm cubes and the Desiree slightly smaller (2.5cm) as the sweet potato will cook more quickly. Halve the red onion then cut the half into 4-6 segments, discarding any tough outer skin. De-seed the peppers and cut into 2.5 cm squares, and separate the cloves of garlic.
Put everything into a large roasting tin or whatever you want to use (it should be big, otherwise use two dishes) and, using your hands, give the vegetables a good coating of olive oil. Season with black pepper, but no salt as the cheese will make it salty (and anyway, the salt will make water leech out).
Cook for 45 minutes, by which time the vegetables should be cooked through and here and there tinged with brown.
You'll need to turn the oven up to maximum, or light the grill for the endgame: so place the thinly sliced cheese on top of the bake, and put it back in the very hot oven or under the grill until the cheese has melted and turned slightly brown on top, about 5-10 minutes. Serve straight out of the roasting tin.
Produces: 2-3 Servings