Boil some water. Then put the dry bread in a bowl and pour the hot water over it. The water should cover the bread. Let it sit for about 5-10min depending on the size of the bread pieces. When the bread is soft put it in a strainer and carefully press out the water.
Thaw and drain the spinach and dice your tomatos, onions and garlic and anything else you like to add like capers or olives.
Add the onions and garlic to the bread in the bowl along with some salt and pepper and other spices that you might like (e.g.mustard)
Mix all the ingredients together. Most likely your bread patty mix will still be pretty soft, meaning there is a too much liquid in it. We'll fix that with my Oma's way when she made meat balls: add a handful or two of oats. With this amount you need 3-4 handfuls. You can use normal oats or quick oats, both work. They will soak up any extra liquid.
When the bread patty mix has the right consistency, add the tomatos and spinach. As tomatos contain quite a bit of liquid you might want to drain them first. Again, if there is too much liquid in the mix use Oma's trick.
Now fry the patties until golden brown on both sides.