Shred zucchini in a food processor. Place onto a plate covered with paper towels and pat or squeeze out as much moisture as possible. Toss into large bowl.
Add ground turkey, flaxseed, garlic and onion powders, salt, and pepper. Mix well and shape into 4-5 patties.
Drizzle a small amount of oil onto a skillet or griddle and heat over medium-high. Swirl oil around to coat evenly. Cook burgers 3-4 minutes per side or until no longer pink.
Meanwhile, shred lettuce and slice the tomato and avocado; set aside separately.
Place each burger onto a bun and top with lettuce and sliced tomato and avocado.
Serve with mango cubes.