Peel the sardines. Cut the vegetables into slices. Put a layer of potatoes, a layer of tomatoes, a layer of onions in a saucepan.
The sardines are placed over these layers. Put the rest of the vegetables over the sardines and at the end the sliced lemon, salt, pepper, bay leaves and thyme. Cover with a lid.
For the first 5-6 min. boil over high heat, and then over medium to low heat for. another 25-30 min.
After boiling, let it rest for 15 minutes to mix the flavors