Salt
12 ounces long, thin pasta, such as bucatini, spaghetti or linguine
3 tablespoons extra-virgin olive oil
3 garlic cloves, thinly sliced
3 scallions, thinly sliced, white and green parts separated
6 to 10 anchovies, chopped
3 tablespoons drained capers
1 cup torn fresh herbs, such as parsley and dill, or celery leaves, plus more for serving (optional)
1 (5- or 6-ounce) can tuna, drained
Red-pepper flakes, for serving
Lemon wedges, for serving
In a well-salted pot of boiling water, cook pasta according to package directions until al dente. Drain, saving 1 cup pasta 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 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.
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.