Preheat the oven to 450F. Line a baking sheet with parchment paper. Add the sweet potato, olive oil, and salt. Toss to coat well, then spread out into an even layer. Bake for 20 minutes or until nicely browned.
In a medium microwavable bowl, add the beans. Microwave for 30 seconds to warm them up (warming them helps them absorb more flavor). Add vinegar, salt, and pepper and toss to coat.
In a jar with a tight-fitting lid, add the oil, vinegar, mustard, soy sauce, pepper, and salt. Shake vigorously to combine.
Add kale to a large bowl along with about ¼ cup of the dressing. Use your hands to massage the dressing into the kale (you’ll notice it brightens in color and wilts down a bit). Divide between your bowls. Add sweet potatoes, beans, egg, avocado, feta (if using), and pickled red onions. Drizzle remaining dressing all over. Sprinkle the egg and avocado with some salt and grind some black pepper all over. Dig in!