Add the olive oil to a large heavy pot or Dutch oven set over medium heat. Add the onion and shallots and mix well to combine. Sauté for approximately 5 minutes, or until the onions start to soften and turn translucent. Stir often.
Stir in the diced bell pepper and continue to cook for 4-6 minutes, stirring often.
Add the garlic and cook for 1-2 minutes, stirring continuously, before adding the dried oregano, Italian seasoning, salt, pepper, and crushed red pepper. Mix well to combine.
Mix the tomato paste with the cooked onions, stirring constantly to prevent burning. Allow the tomato paste to cook with the onions for 1-2 minutes.
Increase to high heat and add the white wine, crushed tomatoes, bay leaf, and fish/clam broth. Mix well and bring to a low boil. Cover and reduce heat to low. Simmer for approximately 25 minutes.
TIP: you may make this homemade tomato-based broth ahead of time. If you choose to make it ahead of time, stop cooking and store in the refrigerator before adding any type of seafood.
Still simmering, add the clams and mussels to the pot. Cover, and cook until the clams and mussels begin to open (approximately 5-10 minutes). Discard any clams and mussels that do not open. Add the calamari and fish and cook for 5 minutes, gently mixing to combine. Next, add the scallops and shrimp, and cook, covered, for 5 minutes. Last, but not least, add the crab legs to the pot and cook for 5 minutes, or until heated through.
Season with additional salt and pepper, to taste, and garnish with fresh parsley and parmesan cheese. Serve with crusty bread (including sourdough bread or French bread), or, mashed potatoes (not traditional, but amazing!) Enjoy!