Preheat the oven to 350 degrees. Cook and stir the ground turkey and onion in a nonstick skillet until brown. Transfer to a colander and rinse with hot water to wash away any excess fat. Shake dry. Spread half cup of the salsa in the bottom of ungreased square baking dish. Mix the remaining salsa, the sour cream, soup, and pimientos. Layer half the tortilla strips, turkey mixture, soup mixture, and cheese in the baking dish. Repeat. Bake uncovered until the casserole is hot and bubbly, about 30 minutes. Let stand 10 minutes. Garnish with olives if desired.