Chop the vegetables and cook them together into a pot (make sure the onion is more finely sliced). Add two glasses of water, some olive oil and a pinch of coarse salt. Slow cook for 20 mins, with the lid on, shaking the pot from time to time to prevent sticking. If needed, add a little water. Halfway through the cooking or at the end, add the pecorino cheese. Serve lukewarm, preferably with slices of toasted bread.