Heat oil in a Dutch oven coated with cooking spray over medium-high heat. Add onion and next 4 ingredients; sauté 5 minutes. Add wine and tomato. Bring to a boil; reduce heat, and simmer, uncovered, 5 minutes.
Add shrimp and halibut to pan. Cover and simmer 5 additional minutes or until shrimp are done and fish flakes easily when tested with a fork.
Tip: If you're buying unpeeled shrimp, you'll need to buy 1/2 pound to get 6 ounces of peeled and deveined.