Coat a large nonstick skillet with cooking spray; place over medium-high heat until hot.
Add onion, bell pepper, and garlic; saut until tender.
Add tomatoes, lemon juice, oregano, and pepper; reduce heat, and simmer 2 minutes.
Add fish, spooning tomato mixture over fish. Cover and simmer 10 minutes; add olives. Cover and cook 4 minutes or until fish flakes easily when tested with a fork.