Preheat oven to 450 degrees F. Combine oil, tamari, salt and lemon juice in a small bowl to make a marinade.
In a large baking dish, combine onions, red bell peppers, green bell peppers and garlic with half of the marinade. Set aside to let marinate at room temperature for about 10 minutes.
In a large bowl, combine mahi mahi and shrimp with remaining marinade. Cover and refrigerate for about 20 minutes.
Bake vegetables until just tender, about 20 minutes, then remove from oven. Add mahi mahi and shrimp to baking dish with vegetables and toss gently to combine. Return to oven and cook until shrimp are curled and mahi mahi is opaque, about 10 minutes more.
Serving includes 1/4 of mahi mahi, 1/4 of shrimp, 1/4 of vegetables and 1/2 cup brown rice for a Curves Complete Phase II lunch or dinner. You can add a salad with 2 T of any Fat Free salad dressing.