In a well-salted pot of boiling water, cook pasta according to package directions until al dente. Drain, saving 1 cup pasta water. I use a tablespoon of salt in my water.
In a large skillet, heat the oil over medium. Add garlic and scallion whites, and cook until fragrant, about 1 minute.
Add anchovies and capers and cook until anchovies melt and capers and garlic turn golden, 2 to 3 minutes longer.
Add ½ cup pasta water, let it reduce until there is just a little left in the pan, then add pasta and herbs and toss well to coat.
Add tuna and toss well.