Heat a griddle pan until smoking. Lightly brush the bread with 1 tbsp oil and griddle on each side for 1-2 minutes until charred nicely. Cut the bread roughly into crouton cubes and set aside.
Heat the remaining oil in a large deep frying pan. Add the onion and cook for 5-6 minutes, until softened but not coloured. Add the remaining vegetables and tomatoes, season well, then cook for 8-10 minutes until the tomatoes have started to cook down. Stir in the garlic and red wine vinegar and cook for another minute.
Meanwhile, whisk together the eggs, milk and 2 tbsp of the Parmesan and season.
Preheat the oven to 180°C/gas mark 4. Assemble your strata by spooning a little of the veg mixture into an individual pie dish or ramekin. Cover with croutons, then sprinkle over some feta, mozzarella and a little Parmesan. Top with more veggies and croutons, then pour over the egg custard and sprinkle a little more Parmesan on top. Repeat this 3 more times into individual dishes.
Bake in the oven for 30-35 minutes, until the topping is golden brown.