Meanwhile, in a large heat proof bowl, combine the parsley, lemon zest, red pepper flakes, and salt.
In a small saucepan over medium heat, combine the olive oil, butter and garlic. Once the butter is bubbling, pour it over the parsley mixture. Stir to combine.
Add the cooked linguine to the bowl along with the lemon juice and the reserved pasta water. Use tongs to toss the pasta until combined and fully coated.