First of all, preheat the oven to 350oF.
Now mix the Garlic, Chicken, Feta Cheese, Oregano, Shallots, Spinach, Salt, and Pepper in a bowl and leave it to chill until it is ready to grind.
Then grind the mixture using a meat grinder. Then put it in a bowl (priorly placed in ice).
Add the remaining Feta, Vinegar, and Lemon Juice and mix it at medium speed until liquid is mixed well.
Put a frying pan with a little quantity of oil in it and place over medium to high heat. Then make a small sausage patty and fry it until it is completely cooked through.
Adjust the taste of sausage if required by seasoning it.
Then stuff this sausage in the hog casing and twist it to give it a final look. You can refrigerate the remaining patties to cook them later.
Prepare a coal grate, evenly spread the lit burning charcoal, cover the grill, and heat it up for about 5 minutes. Then clean the grate and grease it with some Oil.
Now grill the prepared treat over direct heat that should be almost medium to high, until the sausage shines.
Now remove it from the grill and cool it for almost 5 minutes. It is all set to be served.