Heat olive oil in a large pot over medium-high heat. Add chopped onions. Cook for 5 minutes. Add garlic and tomatoes. Cook for an additional 5 minutes.
Add liquid, herbs and seasonings. Bring to a moderate boil for 10 minutes.
Finally add cooked lobster meat, shrimp, mussels and flounder (or other white meat fish). Stir gently. Cover and bring to a boil for an additional 5-10 minutes. The mussels are done when they have opened. If some do not open, discard. The shrimp will turn an opaque color with a hue of pink and the flounder will be flaky and white.
Remove from heat. Serve warm with fresh bread and Parmesan cheese, if desired.
**I used Bar Harbor seafood stock. The original recipe calls for clam juice. If you cannot find seafood stock, use 2: 8oz jars of clam juice instead. Seafood stock will be located near the other stocks and broths. Clam juice should be near the canned fish.Adapted from Mastering the Art of French Cooking by Julia Child