Heat oven to 190C/170C fan/gas 5. Halve the 2 part-baked gluten free baguettes lengthways and cook directly on the oven shelf for 8 mins.
Meanwhile mix the diced peppers, tuna, and 75g of the grated cheddar.
Transfer the gluten free baguettes to a baking tray, spread each with 1 tbsp tomato purée, divide the tuna mix over, top with tomato then sprinkle with the remaining grated cheddar. Bake for 12 mins until melting and golden.