Peel and slice the onion. Wash the peppers, remove the stalks, seeds and inner white filaments and cut them into small diamond shapes. Wash the courgettes, trim them and cut them into slices. Wash the cherry tomatoes and cut them in half. Rinse the corn. Heat 4 tablespoons of oil in a non-stick pan; add the onion, season with salt and fry for a couple of minutes.
Add the pepper and after 5 minutes the courgettes. Continue cooking over high heat for another 3-4 minutes until the courgettes start to brown, add the cherry tomatoes and, after a minute, the corn. Scent with a few chopped basil leaves, season with salt and pepper, stir and remove from the heat.
Turn on the oven at 180° and line a baking tray with baking paper. Remove the rind from the Fontina and cut it into slices. Cut the baguette in two parts and then in half lengthwise and cover each piece with the Fontina slices.
Bake the baguette for 5 minutes until the cheese starts to melt, when out of the oven stuff it with the ratatouille and put it back in the oven for another 2 minutes. Serve hot garnished with more basil leaves.