Preheat oven to 425F and spray a large sheet pan with cooking spray.
In a small bowl, stir together topping ingredients. Set aside.
Pat fish dry with a paper towel. Place on sheet pan and season with salt and pepper. Top each filler liberally with yogurt sauce. You can use leftovers for serving.
Arrange red onion, tomatoes, zucchini, lemon, and capers on sheet pan, evenly covering fish and surrounding space. Drizzle with olive oil. Season with a pinch of salt, pepper, and za'atar.
Bake for 20 minutes, or until snapper is cooked through. Serve over brown rice with a big green salad!
