Lay cabbage on its side and cut 2 slices crossways through the middle, each about 2cm thick. Do not remove outer leaves at this stage. Place on oiled baking tray and pour 1 tablespoon of oil over each; season with salt and pepper.
Cook for 25 minutes in preheated oven.
Place tomatoes and juice in a non-stick pan and cook over high heat for 8 minutes. Stir constantly for the next 5 minutes with a wooden spoon. The mixture should be reduced to 2 heaped tablespoons of intensely flavoured paste.
Preheat oven grill to high.
Remove cooked cabbage from the oven. Top each with crumbled blue cheese and grill 8cm from heat for 2 minutes. Using a fish slice, transfer to warm plates and top with splash of tomato paste.