Prep the string beans. Wash, drain and trim off the stems and bottom ends of the beans.
Place a dry skillet over medium heat. Add the cashew nuts and toast for 2–3 minutes, stirring often until golden and aromatic. Remove and set aside.
Add the chive garlic butter to the same skillet. Once melted, add the sliced garlic and cook for 1 minute, stirring to release its flavor into the butter.
Add the trimmed string beans and toss to coat in the flavored butter. Cook for 2–3 minutes, stirring occasionally.
Season with sea salt, black pepper, and chili flakes if using. Add the sliced garlic for additional garlic flavor. Add the water, cover the skillet, and allow the beans to steam for 2–3 minutes until just tender but still vibrant.
Uncover, stir in the toasted cashews and lemon zest. Add lemon juice if using. Sauté uncovered for 1 additional minute to blend flavors and reduce any liquid.
Taste and adjust seasoning to your preference. Serve warm as a side dish.