Prep the scapes: Rinse, trim dried tip and bottom. Cut into 2- to 3-inch lengths. If thick, split lengthwise.
Boil pasta water: Fill pot with 4 quarts water, salt generously (2 tbsp kosher salt). Bring to a rolling boil.
Blanch scapes: Drop cut scapes into boiling water for exactly 1 minute until bright green and tender. Transfer to a plate with a slotted spoon. Let cool, then roughly chop into 1-inch pieces.
Cook pasta: Add pasta to same boiling water, cook until al dente (1-2 min less than box). Before draining, reserve 1 cup pasta water. Drain pasta, do not rinse.
Toast breadcrumbs: While pasta cooks, heat 2 tbsp olive oil in skillet over medium heat. Add panko and red pepper flakes, stir constantly until pale gold, about 2 minutes. Transfer to a small bowl, season with salt.
Combine: In same skillet, add remaining 2 tbsp olive oil, chopped scapes, and 1/4 cup reserved pasta water. Heat over low heat 1 minute. Add drained pasta, toss with tongs, adding more pasta water as needed for a light coating.
Finish: Remove skillet from heat. Add Parmesan, toss vigorously until melted and creamy. Taste and adjust salt. Squeeze a little lemon juice if desired. Transfer to serving bowls.
Top: Sprinkle toasted breadcrumbs over each bowl, then lemon zest and extra Parmesan. Do not stir in.