Sauté onion and fennel until translucent. Add cherry tomatoes, red pepper flake, pesto, and marinara; stir well to combine. Add white wine, dry vermouth, or water to desired consistency.
Season snapper with lemon pepper and Italian seasoning.
Place pomodoro sauce in sauté pan. Place thawed snapper on top of sauce, cover with parchment paper or lid. Cook until snapper is just cooked through.
Add fresh herbs, stir, and remove sauce to serving plate.
Place snapper on top of sauce and arrange warm mussels around fish.
Cut each piece of toasted bread in half on a diagonal and use as garnish.
