Preheat the oven to 180 degrees. Place the peppers in an oven dish and put it in the oven for an hour.
After an hour, parts of the peppers' skins will be black and you can remove the dish from the oven. Let the peppers cool for a bit.
Meanwhile, peel the skins from the onion and cut it into thin rings. Peel two garlic cloves and cut them into thin slices.
Heat some olive oil in a baking pan and fry the onion shortly over high heat and then reduce the heat to very low to let the onion and garlic simmer for about 15 minutes with a lid on the pan.
In the meantime, peel and deseed the peppers under the cold tap. Cut or tear them into about 6 pieces per pepper (but don't worry if they tear into more while peeling).
Add a dash of white balsamic vinegar to the onions and garlic and let it simmer for another 15 minutes.
Then remove the lid from the pan and add the peppers. Leave the pan on the heat without the lid for another 5 minutes.
In the meantime, roast the pine nuts and cut the basil leaves into thin strips. Cut some slices of bread and toast them in a toaster or the oven. Scrape it over a little with a clove of garlic if you like.
Finally, season the peppers with salt and pepper and plate by placing the pepper-onion mixture in the middle of plates and sprinkling the basil and pine nuts over it. Tear the mozzarella or burrata into pieces and divide it around and over the pepper and add a few capers and your crostini. Drizzle some more oil over your mozzarella or burrata and you're ready to serve!