Tiella was the brought to Puglia by the Bourbons. The round tin or copper baking tins that it is cooked in (or more traditionally, terracotta) are also called tiella, taieddha or taeddhra. These casseroles are now baked in the oven but before the days of electric and gas ovens, they were baked on Sundays in wood stoves with a cover on which coals would be layered to ensure that the layers cooked evenly.
There are many variations of tiella, the most famous being tiella barese with layers of baked rice, onions, potatoes, mussels, fresh tomato and Pecorino cheese from Bari. In Salento courgettes (zucchini) and parsley are added. In Foggia, where my husband's grandfather is from, fried salt cod is layered with sliced potatoes, minced garlic, parsley, onions and halved cherry tomatoes. Other economical fish and seafood are also substituted such as octopus, anchovies and sardines. There are also vegetarian versions where the mussels or fish are substituted with oyster mushrooms (cardoncelli) or is simply a baked casserole of peppers, aubergines (eggplant), potatoes and tomatoes. Sometimes artichokes are added. There is even a version with horse meat from Bari. The more ingredients that are included, the more layers there are and the taller the tiella.