Make the toasted panko topping first. Cook the pasta next, adding the broccoli at the last 2 to 3 minutes of cooking time. Drain the pasta and broccoli and set aside.
Cook the shallot and garlic in melted butter. Whisk in the flour. Pour in the broth and whisk.
Stir in the heavy cream, Italian seasoning, red pepper flakes, and lemon zest. Simmer and stir in the Parmesan. Then, stir in the lemon juice.
Add the pasta and broccoli, then stir. Remove from heat and season. Serve with toasted panko topping and extra Parmesan cheese, if desired.