This has long been a favorite way to eat mustard greens, from epicurious.com
2 tbsp olive oil
1 small bunch mustard greens, stems trimmed, leaves cut into half inch strips
1 tbsp finely chopped garlic
4 large eggs, beaten to blend
1 1/2 cups diced fontina cheese
Preheat broiler. Heat oil in medium broiler proof skillet over medium-high heat. Add greens, stir until wilted and tender, about 2 minutes. Add garlic; stir 1 minute. Sprinkle generously with salt and pepper. Pour eggs over greens, stir to blend. Sprinkle with cheese. Cover skillet; cook until fritatta is almost set but top is still runny, about two minutes. Sprinkle with cheese. Place skillet under broiler. Broil until top is set and cheese bubbles, about 1 minute. Cut around frittata to loosen. Slide out onto a plate. Serves 2.