Preheat oven to 180°C. Grease a 6 hole regular muffin tin or line with paper cases.
Heat olive oil in a frying pan on low heat. Add the onion and sauté on low heat, stirring occasionally for 5 minutes so the onion softens but not browns. Add the zucchini and sauté for another 5 minutes then take off heat and put to one side. In a bowl, gently whisk the eggs, ricotta and herb until just combined. Then gently mix in the onion and zucchini. Using a soup ladle, fill each muffin hole with egg mixture. Sprinkle with parmesan and bake for 15-20 minutes, until the frittata feels firm. Cool in tin for a few minutes then serve with bread, toast or cooked grain and vegetables.
Best eaten on the day but keeps well in the fridge for 1 day.