Mix the oil and eggs. Put the flour, turmeric and zest in a food processor, add the oil and egg mix, and blend to a crumbly dough (it may require extra flour or oil). Once the dough has come together and is smooth (you may need to work it a little by hand, too), divide it into four thick, rectangular blocks. Wrap in clingfilm and chill for anything from 30 minutes to two days.
Dust a work surface with flour. Take a piece of dough and flatten with a rolling pin. Set a pasta machine to its widest setting and pass through. Repeat, narrowing the setting a notch each time, until you reach the lowest setting. Place pasta sheets flat under a moist towel, so they don't dry out.
Use a fork to crush all the filling ingredients together, apart from the egg white. Use a pastry cutter (or rim of a glasto stamp out pasta circles roughly 7cm in diameter. Brush each with egg white and place a heaped teaspoon of filling in its centre. Place another disc on top and, with fingers dipped in flour, squeeze out any air as you bring the edges of the discs together. You should end up with a pillow-shaped centre surrounded by a 1cm edge. Tighten the edges until you can't see a seam. Repeat with the rest of the dough, place the ravioli on a tray sprinkled with semolina, and leave to dry for 15 minutes. If you'd like to make it ahead, you can cover them with plastic wrap and leave in the refrigerator for up to two days.
To serve, bring a large pan of salted water to the boil. Cook the pasta for two to three minutes, until al dente, drain and divide between four plates. Sprinkle with pink peppercorns, tarragon and lemon zest. Drizzle with olive oil, add salt and a squirt of lemon juice (if desired), and serve piping hot.
