Preparation Toast grains in a dry medium heavy pot over medium heat, stirring occasionally, until just slightly darkened and beginning to smell nutty, about 4 minutes. Pour in 4 cups water, then add onion, garlic, lemon zest, and a couple of big pinches of salt; stir to combine. Bring mixture to a boil, then reduce heat to medium-low and simmer, stirring occasionally and skimming any foam from surface as needed, until grains are tender (pull out a few grains and take a bite to test), 35–45 minutes; pluck out and discard onion, garlic, and lemon zest. Meanwhile, purée parsley, dill, buttermilk, and a big pinch of salt in a blender until bright green and smooth. Pour into a medium bowl, add yogurt, and whisk until your arm gets a bit tired—3 minutes should do the trick (whisking the mixture well will ensure that the yogurt doesn’t split and get grainy when you add it to the grains). Pour buttermilk mixture over grains. Increase heat to medium and bring to a bare simmer. Cook just until heated through, about 1 minute. Remove from heat and squeeze in juice from lemon half. Stir well, then taste grains and season with more salt if needed. Skim any foam from surface. Ladle grains into bowls. Drizzle some oil into each bowl and top with coarsely ground pepper.