Lightly beat the eggs with a fork. Stir in 11/2 tablespoons of cold water and the chives. Season, then set aside.
Heat the oil in a large heavy-based frying pan. Add the zucchini and cook over a moderate heat for 3–4 minutes, stirring occasionally, until lightly golden on both sides and just tender. Add the garlic and cook for a few more seconds.
Add the tuna and peas and stir to break up the tuna into chunks. Pour in the beaten egg mixture, and work quickly to mix it into the other ingredients, then stop stirring.
Reduce the heat slightly and cook the frittata for 7 minutes, or until the base is golden. Take a large plate and place it upside down over the pan. Wearing oven gloves, quickly invert the frittata onto the plate. Slide the frittata back into the pan and continue cooking for 3–4 minutes until golden brown on the second side. (Alternatively, you can finish it off under a moderate grill for 5 minutes, if cooked in a pan with a heatproof handle. In this case, do not invert it.)
Remove the pan from the heat and cut into wedges to serve.
• For a more substantial frittata, leftovers such as diced cold potato or cooked beans or pulses may be added. Other vegetables could also be included. * • For an easy family supper, serve with a salad and crusty bread or boiled potatoes.