How to Make It
Heat oven to 425° F. Oil a 9-inch pie plate. Toss the cauliflower with the paprika, 2 tablespoons of the oil, ½ teaspoon salt, and ¼ teaspoon pepper on a rimmed baking sheet. Roast, tossing once, until browned and just tender, 15 to 18 minutes. Let cool for 5 minutes. Spread evenly in the pie plate.
Whisk the eggs, milk, cheese, parsley, and ½ teaspoon each salt and pepper in a medium bowl. Pour over the cauliflower. Bake until the top is golden and the custard is just set in the center, 25 to 30 minutes. Let cool for 5 minutes.
Whisk the vinegar, the remaining tablespoon of oil, and ¼ teaspoon each salt and pepper in a large bowl. Add the greens and toss. Serve with the frittata.