Cook the pasta according to the package directions. Reserve ½ cup of the cooking water; drain the pasta.
Wipe out the pasta pot. Add the oil, garlic, and red pepper and cook over medium heat, stirring frequently, until fragrant, 2 to 3 minutes.
Add the pasta, tuna, lemon zest, ¾ teaspoon salt, ½ teaspoon black pepper, and the reserved pasta water and cook over low heat, tossing, until the sauce is slightly thickened and coats the pasta, 1 to 2 minutes.