Heat 2 tablespoons olive oil in a Dutch oven or large saucepan until shimmering. Add 2 cups of asparagus and chile flakes, and cook until lightly browned, about 4 minutes. Season with salt and pepper and set aside.
In the same saucepan, add the farro and stock and bring to a simmer. Season with salt and cook until farro is tender, about 30 minutes; add water if necessary to keep farro covered. Drain farro and transfer to a large bowl. Stir in peas and kale and let stand until peas are tender and kale is wilted.
Meanwhile, in a medium bowl, whisk together the remaining 4 tablespoons olive oil along with the lemon juice and mustard. Season with salt and pepper. Fold vinaigrette into farro, add the cooked asparagus, almonds, scallions, feta, and remaining ¼ cup raw asparagus. Let stand 5 minutes, then toss and serve.
