Heat olive oil in a large saucepan over high heat until shimmering.

Add diced fennel salami and cook, stirring, for 30 seconds.

Add thinly sliced fennel bulb, onion, and garlic. Reduce heat to medium, season with salt and pepper, and cook, stirring, until vegetables are softened but not browned, about 5 minutes.

Add saffron and red pepper flakes and cook until fragrant, about 30 seconds.

Add pastis, orange zest, and crushed tomatoes.

Increase heat to high and bring to a boil.

Add mussels, stir, cover, and cook, shaking pan constantly and peeking every 30 seconds to stir.

As soon as all the mussels are open, transfer mussels to a bowl using tongs. Place pan lid over bowl to keep mussels warm.

Remove from heat and whisk in parsley, butter, and lemon juice.

Return mussels to pot, stir to combine, then transfer to a warm serving bowl.

Serve immediately with broiled bread.