Preheat broiler to 350 degrees F. Cook potatoes and cut into bite sized pieces.
In a large oven proof pan, heat olive oil and saute onion. Then add garlic and Swiss chard and cook until Swiss chard is just wilted. Add potatoes, salt and pepper and stir. Pour beaten eggs evenly over the vegetables. Cook over medium heat until the eggs are set on the edges and loosely set in the middle. Sprinkle diced tomatoes over the top and cover with cheese.
Place pan under the broiler for 2-3 minutes or until the center is set and the cheese is melted. Slice and serve.