In 3-quart saucepan or Dutch oven, melt butter over medium heat. Add onion and garlic; cook and stir 2 to 3 minutes or just until garlic begins to brown.
Stir in all remaining ingredients except fish. Heat to boiling. Reduce heat; cover and simmer 8 minutes.
Add fish; cook uncovered 5 to 7 minutes, stirring occasionally, until fish flakes easily with fork and vegetables are tender.