In a large skillet, heat the olive oil and 1 tablespoon of the butter over medium heat. Add the watermelon radishes, sea salt, and 2 teaspoon of the fresh rosemary to the pan.
Cook for 10-12 minutes, stirring occasionally, until the radishes are tender and slightly browned. It may take a few more minutes depending on your stovetop, so adjust the cooking time as needed.
Add the last tablespoon of butter and the last teaspoon of rosemary, as well as the lemon zest, to the skillet. Cook for another couple of minutes. Remove from heat and serve warm!
Notes
Feel free to adjust the seasonings as desired (i.e. more rosemary, less butter, more lemon, etc.)