• 2 tablespoons olive oil
• 8 tablespoons (1 stick) unsalted butter, divided
• 1 garlic clove, crushed
• 1/2 teaspoon crushed red pepper flakes, divided
• 3/4 cup panko (Japanese breadcrumbs)
• 1 teaspoon finely grated lemon zest
• Kosher salt, freshly ground pepper
• 12 ounces fresh strozzapreti or other fresh or dried pasta
• 2 bunches flat-leaf spinach, trimmed, large leaves torn in half (about 8 cups), divided
• 1 tablespoon (or more) fresh lemon juice
• 1 tablespoon (or more) thinly sliced preserved lemon peel