Heat the olive oil in a large pot or Dutch oven over medium high heat. Add the fennel and saute for 5 to 7 minutes or until beginning to soften. Add the garlic and cook for a minute or two until fragrant. Add the white wine and let cook for a few minutes, stirring often, until nearly evaporated. Add the hand-crushed tomatoes and their juices, stock, and saffron and bring to a boil. Reduce heat and let simmer for 15 minutes.
Add the seafood and let simmer until opaque, about 3 minutes. Let sit, covered for 3 to 5 minutes. Stir in the parsley, red pepper flakes, and orange zest. Season with additional salt and pepper if desired. Serve in big bowls, drizzled with olive oil and garnished with fennel fronds.
OPTIONAL: Add 12 to 24 mussels (scrubbed and de-bearded) along with the other seafood. Cover and let simmer for 3 minutes. Turn off the heat and let sit for another five minutes or so, until the mussels have opened and the seafood is cooked through. Remove any mussels that have not opened. Stir in the remaining ingredients and serve immediately.