1. Preheat oven to 350°.
2. In a large nonstick skillet, heat 1 tablespoon oil over medium-high heat. Add onion and cook, stirring, until soft (about 4 minutes). Add pepper flakes and half of greens and cook until wilted and crisp-tender (about 5 minutes); place sautéed greens in a colander. Repeat with remaining greens. Cool slightly and squeeze dry; transfer to a bowl. Using paper towel, wipe out skillet and reserve.
3. In a large bowl, whisk together eggs, Parmesan, and 1/4 teaspoon each salt and pepper until smooth. Add to bowl with greens, vinegar, ricotta, and 1/8 teaspoon pepper; stir to combine. Fold the ricotta mixture into egg mixture.
4. In reserved skillet, heat 1 tablespoon oil over medium heat. Pour egg mixture into pan and cook until the sides are set (about 8 minutes). Transfer to oven and bake until completely set (about 15 minutes).
5. To make pesto: Combine basil, parsley, mint, garlic, and pine nuts in a food processor and process until all ingredients are coarsely chopped. With the motor running, slowly add the remaining 1/3 cup oil and season with 1/4 teaspoon each salt and pepper.
6. Remove frittata from oven and invert onto serving platter. Slice into 8 wedges and serve with pesto.