Heat oven to 375 degrees. Spread pecans on a baking sheet and toast until golden brown, about 8 minutes. Immediately transfer to a medium bowl and stir in raisins, garlic, lemon zest, and 2 tablespoons oil. Season with salt and set aside.
Place broccoli in a pot just large enough to hold it and cover with cold water. Bring to a boil. Reduce heat to medium and cook until broccoli is falling apart and stalks are very tender, 8 to 10 minutes. Drain, reserving 1/4 cup cooking liquid, and return to pot. Stir in remaining 3 tablespoons oil. Gently mash broccoli with a wooden spoon, adding reserved water until creamy. Season with salt and keep warm.
Reduce oven to 275 degrees. On a lightly oiled baking sheet, season fillets with salt and cook, depending on thickness, about 15 minutes (or until just opaque).
To serve, divide puree among plates, top with fillets, and garnish with salsa.