Combine the pasta, cherry tomatoes, onion, olives, oil, garlic, red chile flakes, 1/2 teaspoon salt, and several grinds of black pepper in the pot. Add 2 3/4 cups water and stir to combine. Place the tuna on top of the pasta mixture but do not submerge it.
Lock on the lid, select the Pressure Cook function, and adjust to Low pressure for 6 minutes. Make sure the steam valve is in the “Sealing” position and that the “Keep Warm” button is off.
While the pasta is cooking, stack the basil leaves, roll them up tightly as you would a sleeping bag, and slice crosswise into thin ribbons.
When the cooking time is up, quick-release the pressure. Remove the lid. Add the basil, lemon zest, and lemon juice to the pot and stir, breaking up the fish into bite-size chunks. Season with salt and black pepper.
Let the pasta stand in the pot set in the appliance, uncovered, for 5 minutes to allow the sauce to thicken before serving.