In a well-salted pot of boiling water, cook pasta according to package directions until al dente. Drain, saving 1 cup pasta water.
Step 2
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 1/2 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.
Step 3
Serve with red-pepper flakes on top, more herbs, scallion greens, and a drizzle of olive oil. Serve with lemon wedges on the side for squeezing.