Bring a large pot of salted water to a strong boil. And the pasta and stir to avoid sticking.
When the pasta is just cooked though and slightly short of al dente, carefully remove 1 cup of cooking water and set aside. Drain the pasta. Do not rinse.
Add the pasta back to the pan. Pour over 1/2 cup pesto, and 1/4 cup pasta water, tossing to combine. Add additional pesto if a stronger flavor is desired, or additional pasta water to thin the pesto and coat the pasta.
Allow to sit for 3-4 minutes for the pasta to absorb the pesto, stirring occasionally.
Meanwhile lightly drain the tuna and add to a medium bowl along with2 tablespoons pesto, tossing lightly with a fork to break up the tuna and combine it with the pesto.
Serve the pasta with the pesto tuna on top, or stirred directly into the pasta. Top with red pepper flakes if desired
Notes
Store-bought basil pesto makes this recipe super easy and fast, or make your own with my homemade pesto.