Preheat the oven to 180°C or Gas Mark 4. Line a large baking tray with parchment paper. Chop the sweet potatoes into 1in chunks and slice the red onions into thick slices. Add to a large bowl and toss with the olive oil, garlic granules, chili flakes, salt, and pepper. Transfer to the baking tray and roast for 40 to 45 minutes, until tender and crisp. Stir the tray well halfway through. Allow to cool slightly.
Cook the buckwheat according to package instructions. Allow to cool briefly while you prepare the rest of the salad.
Add all the vinaigrette ingredients with some salt and pepper to a glass jar with a lid. Seal the lid and shake the jar to mix the ingredients together.
Add the kale to the same large bowl (no need to rinse it out). Add 1 tablespoon (15ml) of the vinaigrette. Massage the kale with your hands for 1 minute to wilt the leaves; they will turn vibrant green.
To the kale, add the cooked buckwheat, butter beans, most of the sun-dried tomatoes, and the roasted sweet potatoes and red onions. Pour over most of the dressing and toss well.
Serve in a large bowl or four smaller bowls topped with the remaining sun-dried tomatoes. Sprinkle over the feta cheese, almonds, and the extra dressing.
Eat right away, or cover well and keep in a sealed container in the fridge for 2 to 3 days.