Bring a large pot of salted water to a boil. Add pasta and cook until al dente according to package instructions, about 8–10 minutes. Before draining, reserve 1/2 cup pasta cooking water, then drain and set pasta aside.

While pasta cooks, melt butter in a large skillet over medium heat. Add garlic, red pepper flakes, salt, and pepper. Cook, stirring often, until fragrant, about 30 seconds.

Stir in Parmesan cheese, lemon zest and juice, lemon pepper seasoning, and 1/4 cup reserved pasta water. Simmer until sauce thickens slightly, about 1 minute.

Add cooked pasta to the skillet and toss to combine, adding remaining pasta water as needed to coat. Remove from heat, taste and adjust seasoning, then stir in chopped parsley.

Serve immediately, garnishing with extra lemon zest, pepper flakes, and Parmesan if desired.