In a large skillet, warm the oil over medium heat. Add the garlic and cook for about 3 minutes or until just starting to turn golden.
Stir in the red pepper flakes, half of the greens, and ½ teaspoon salt. Cook until the greens have wilted down to make room for the rest, about 3 minutes. Stir in the remaining greens and ½ teaspoon salt. Continue to cook until the greens have all wilted down, about 3 minutes, stirring occasionally.
Stir in the water and lemon or vinegar and simmer over low heat, stirring occasionally, for about 20 minutes or until the liquid has mostly evaporated (you want some liquid to keep it a little saucy). You can increase the heat towards the end to speed things up. If you’d like, stir in the butter until melted to add richness.
Serve topped with toppings of choice (if using) along with some black pepper and a good drizzle of olive oil.