You probably could skip the meat hammer step if your beef liver pieces already are pretty flat (about 0.5cm / 0.2in of thickness).
If they are way too thick, lay them on the cutting board.
Then, cut from one side with a sharp knife until you nearly reached the end of the other side.
Now, you can simply fold out the pieces and have thinner ones.
At step 3 I used frozen spinach which I thawed & pre-cooked in the microwave for about 3 minutes while beating up the liver:
Of course, you may also use different stuffings.
One idea that I’ve had was pizza stuffing with tomato paste or fresh tomatoes, mozzarella cheese & Italian / Mediterranean herbs (oregano, rosemary, thyme). Maybe with some additional ground beef, pepperoni, fried chicken or even pulled pork.