Thaw fish, if frozen. Rinse fish; pat dry with paper towels. Sprinkle fish with salt. Set aside.
In a large skillet cook onion in hot olive oil over medium heat for 8 minutes or until tender, stirring occasionally. Stir in garlic, tomatoes, oregano, and crushed red pepper. Bring to boiling; reduce heat. Simmer, uncovered, for 5 minutes.
Add olives and capers to sauce. Top with tilapia fillets. Return sauce to boiling; reduce heat. Cook, covered, for 6 to 10 minutes or until fish flakes easily when tested with fork. Remove fish. Simmer sauce, uncovered, for 1 to 2 minutes more to thicken. To serve, spoon sauce over fish. Sprinkle with parsley.