The herbs in the ratatouille are typically called Herbes de Provence. However, the ready mixes for Herbes de Provence which you can by are generally very poor quality and taste. I generally use Laurel, Thyme, Satureja, Oregano and Nutmeg. I also add some fresh Basil if I have some. (I realised afterwards I forgot the Garlic, which is cut into small chips and cooked in the mix from the moment we add the onions)
The result of putting all the vegetable together for cooking is generally underwhelming and watery, even if you let the onions brown separately. I cook the eggplant first, because it is the slowest to cook it is very important for taste and texture that it be well cooked. I add a good deal of olive oil with the eggplants and cover them to prevent drying out.
In the meantime, I mince the onions and let them brown in a separate frying pan. While the onions and eggplant are on the heat, I finish peeling-off, rinsing and cutting the other vegetables into pieces. Then I mix the onions with the eggplants and keep them cooking with cover and begin frying the sweet pepper with additional olive oil. Afterwards, I add the sweet pepper in the mix, keeping cooking with cover, and at last begin frying the zucchini with additional olive oil.
Both the sweet pepper and the zucchini are cooked similarly to Carrots "Façon Vichy" or Leeks Fondue (Fondue de Poireaux), but only with a 15 minute active phase. The passive phase goes on in the mix with the other vegetables.
At last, I add the tomatoes and herbs, and I let the whole mix on low heat for at least one hour and a half (90 minutes), without cover for the water from tomatoes to vaporize, and the consistence of the ratatouille be as suites.