Sunday Brunch: Chard and Onion Omelet

Name: Sunday Brunch: Chard and Onion Omelet
Ingredients: 3 tablespoons olive oil; 1 large red or white onion, quartered and thinly sliced crosswise; 1 bunch chard, leaves only, chopped; Salt and freshly ground pepper; 1 clove garlic; 6 to 8 eggs, lightly beaten (8 large eggs would not fit with the other ingredients in my 10-inch frying pan, which slopes into the bottom quite a lot); 2 tablespoons chopped parsley; 2 tablespoons chopped basil; 2 teaspoons chopped thyme; 1 cup grated gruyère; 2 tablespoons freshly grated parmesan