Remove the skin from the salmon fillet and chop into 1-2 inch chunks. Juice two of the lemons and slice the other removing and discarding seeds. Thinly slice the zucchini and red onion with a sharp knife or mandoline.
Add all of the cubed salmon, veggies, dried spices, olive oil, and lemons to a large prep bowl and toss to combine. Cover with foil and marinade in the fridge for at least 20 minutes or as long as 3 hours.
Once salmon and veggies have marinated spray 6 12 inch metal skewers and add all the salmon and veggies to the skewers alternating everything. This isn't required, but it makes the kabobs look pretty.
Spray your grill with cooking spray, then heat it to 350 degrees F. Once the grill has heated, add the kabobs to the grill and cook 3-5 minutes per side. The salmon will turn pink when it is finished and have a bit of a char. Once cooked remove from the grill and serve warm with tzatziki sauce. Enjoy!