Preheat oven to 350 F.
In a large bowl, combine eggs, milk, salt and pepper to taste; set aside.
Heat olive oil in a cast iron skillet over medium high heat . Add garlic and cook until fragrant, about 1-2 minutes. Add potatoes and onion and cook, stirring occasionally, until potatoes have softened and onions have caramelized, about 8-10 minutes. Add kale and cook, stirring occasionally, until wilted, about 2 minutes. Add egg mixture and tomatoes, and cook until the eggs start to set, about 3-4 minutes. Sprinkle with mozzarella.
Place into oven and bake until the top is set and cheese has melted, about 10 minutes. Serve hot, warm or cold. Serves 4 to 6.