Make the tzatziki: Grate the cucumber and use a paper towel or cheesecloth to squeeze out all the extra moisture. Stir it into the yogurt along with the lemon juice, lemon zest, dill, salt, and pepper. Refrigerate for 1 hour or more.
Preheat oven to 325 degrees.
In a food processor, pulse together the onion and garlic until they form a paste. Remove from the food processor and press into a paper towel or cheesecloth to remove excess water.
Combine the ground chicken, marjoram, rosemary, onion and garlic mixture, salt, and pepper in a large bowl.
Form into a small meatloaf and bake on a sheet pan for 50-60 minutes until cooked through. Slice very thinly and enjoy!
