Serves 6 / Serving tip: Accompany this colorful egg dish with quinoa pilaf and a mixed green salad.
1½ tablespoons olive oil, divided
1½ cups (4 ounces) presliced button or shiitake mushrooms
½ cup diced red bell pepper
½ teaspoon minced garlic
2 cups (2 ounces) packed arugula leaves
⅛ teaspoon salt
2 tablespoons chopped fresh dill
½ cup shredded Gruyère cheese
Preheat oven to 400°. Heat a 9-inch ovenproof skillet over medium heat, then add 1 tablespoon oil. Add mushrooms, peppers, and garlic. Sauté until vegetables are tender, 3-4 minutes. Add arugula and stir until wilted, 1-2 minutes. Sprinkle with salt and pepper to taste, then transfer to a plate.
In a medium bowl, whisk together eggs, salt, and dill. Add remaining ½ tablespoon olive oil to skillet, swirling to coat bottom and sides. Pour in egg mixture. Evenly distribute vegetables over eggs, then sprinkle with cheese. Cook over medium-low heat until edges are set (3-4 minutes), then transfer to oven and cook until eggs are set, 7-10 minutes. If some spots remain soft, finish under broiler for 1-2 minutes. Loosen edges of frittata with a rubber spatula and transfer to a serving plate.