Preheat the oven to 325°F. Spread the almonds in a single layer on a small baking sheet and toast for about 8–10 minutes, stirring once halfway, until fragrant and lightly golden. Remove from oven and set aside to cool.
Make the dressing: in a jar or small bowl combine the minced garlic, 1/2 tsp of the sea salt, black pepper, olive oil, balsamic, Dijon and lemon juice. Close the jar and shake vigorously (or whisk) until the dressing is smooth and slightly emulsified. Add the thinly sliced onion to the dressing to let it mellow while you prep the greens.
Prepare the greens: thinly slice the kale across the leaves to create fine ribbons. Shred the Brussels sprouts with a slicer, food processor (slicing blade) or very sharp knife; you want paper-thin strands so they wilt easily with the dressing.
Place the kale and shredded Brussels sprouts in a very large bowl. Sprinkle the remaining 1/4 tsp sea salt over the greens and pour the lemon juice (if any remains) over them. Using clean hands, massage the greens for 2–3 minutes until the kale softens and the Brussels release some moisture.
Drain the onion from the dressing if you prefer less bite, then pour the dressing over the massaged greens. Add the dried cranberries, red pepper flakes and half of the grated Pecorino. Toss thoroughly so everything is evenly coated — a couple of firm tosses is better than gentle stirring here.
Let the salad sit at room temperature for 10–20 minutes to allow flavors to meld and the greens to soften further. Right before serving, fold in the remaining Pecorino and sprinkle with the toasted almonds for crunch.
Taste and adjust: add more black pepper, a pinch of salt, or a drizzle of olive oil or balsamic if you want brighter or richer notes. Serve chilled or at room temperature.