Preheat the oven to 375 degrees Fahrenheit and line a medium baking tray with parchment paper.
Make the glaze. In a small bowl mix together ketchup, Worcestershire sauce (or A1 sauce) and olive oil. Set aside.
Grate zucchini, place on paper towels or on a clean cotton kitchen towel and squeeze out extra moisture over the sink.
Cook onion in butter in a small skillet until transculent (don't brown it). Add minced garlic at the end and cook for another minute, stirring. Set aside to cool.
In a medium or large bowl combine ground chicken, grated and squeezed out zucchini, egg, panko breadcrumbs, 3 tablespoon ketchup, marjoram, cooked onions and garlic, salt and pepper.
Mix all ingredients using a spoon (or clean hands) until evenly combined. Don't overmix.
Form a meatloaf and place on the prepared baking sheet.
Brush with the glaze and place in the preheated oven.
Bake for 45 min at 375 degrees or until meat thermometer inserted in the middle of the meatloaf shows 165 degrees or higher.