Cook pasta per package directions. Reserve 1 cup pasta water, then drain pasta and return to pot. Meanwhile, heat oil in large skillet on medium. Add garlic and cook, stirring, until it starts to sizzle, about 1 minute. Add chicken, season with red pepper flakes and ½ tsp each salt and pepper, and cook, breaking up into very tiny pieces, until nearly cooked through, 4 to 5 minutes. Add wine and simmer until nearly evaporated, about 2 minutes. Add broth and toss to combine, then bring to a simmer. Fold in lemon zest, Parmesan, and herbs. Remove from heat and add butter if using, stirring and tossing until melted. Toss with rigatoni and 1/2 cup reserved pasta water, adding more if pasta seems dry. Top with additional Parmesan if desired.