Vigorously whisk the egg whites in a bowl until they form soft peaks and look frothy and slightly foamy, about 1-2 minutes.
Thinly slice the zucchini and bell pepper, then heat 1 tablespoon of olive oil in a non-stick skillet over medium heat.
Sauté the sliced vegetables in the hot oil for about 3-4 minutes until they soften slightly and become fragrant, then transfer them to a plate.
Add the chopped herbs to the same skillet with a teaspoon of olive oil and cook for about 30 seconds until fragrant, then remove from heat.
Gently fold the sautéed vegetables and herbs into the whipped egg whites, seasoning with salt, pepper, and lemon zest to taste. Be careful not to deflate the whites.
Pour the mixture into the preheated non-stick skillet, spreading it evenly with a spatula. Cook over medium-low heat for about 5 minutes until the edges start to turn golden and the center begins to set.
Cover the skillet with a lid and reduce the heat to low, cooking for another 5-7 minutes until the top is just set and slightly puffed. The edges should be golden, and the top firm but still tender.
Remove the skillet from heat and let the frittata rest uncovered for about 2 minutes to allow it to firm up for clean slicing.
Gently slide the frittata onto a plate and cut into wedges. Serve warm, optionally garnished with extra herbs or a drizzle of olive oil.
