Add the kale and season with salt. Cook over low heat, stirring often, until softened, about 10 minutes. Add the escarole, season with salt and cook, stirring often, until just tender, about 5 minutes longer. Stir in the spinach and cook until wilted, about 3 minutes. Stir in the remaining 2 tablespoons of olive oil, the olives and capers and season with salt and pepper. Fold in the ricotta salata, add the lemon juice and serve.