Preheat oven to 400 degrees. Spray a baking dish with cooking spray.
Season tilapia on both sides with seasonings. Place in baking dish and bake for 8-10 minutes; the lesser of the time if they are thinner filets. Fish will flake when done.
While fish bakes, whisk together yogurt, lemon juice, sugar and olive oil. Toss in a large bowl with spinach, lettuce and tomatoes.