Preheat oven to 400F.
Lay zucchini slices on a paper towel and pat dry.
Line an oven-safe tray with parchment paper and sprinkle a thin layer of cheddar cheese.
Lay the zucchini slices slightly overlapping to form a rectangle, sprinkle with garlic powder (and smoked paprika if desired), then add another thin layer of cheese on top.
Bake for 14-15 minutes until edges are golden and cheese is crisp.
Let cool slightly, then cut in half to make the 'bread' slices.
Spread avocado mayo and mustard on the 'bread' slices.
Layer on the chicken, lettuce, tomato, onion, avocado, and everything bagel seasoning.
Add the top 'bread' slice and slice diagonally.
