In a medium bowl, combine the eggs, salt, 1/2 tsp of lemon zest, and 1/2 tsp of pepper, and beat well with a fork. Mix in 3/4 C of cheese and blend slowly.
In a 10-inch ovenproof frying pan, warm the olive oil over medium-high heat. Add the onion and peppers and saute until almost tender, about 6 minutes. Add the zucchini, sprinkle with the remaining lemon zest and a dash of ground pepper and saute until tender, about 5 minutes.
Pour the egg mixture into the frying pan and gently stir to distribute evenly. Reduce heat to medium-low, cover, and cook until the eggs are nearly set, but still moist in the center, about 9-10 minutes.
While the frittata is cooking, preheat the broiler on high. Sprinkle the remaining cheese over the frittata, place the pan in the oven and broil until the eggs puff and the cheese browns, around 4 minutes. Remove from the oven, then squirt with the lemon juice, sprinkle the torn cilantro over top, cut, serve, and enjoy.