To make the vinaigrette, whisk together the orange juice, lime juice, vinegar, maple syrup, shallot, mint, salt, and pepper, in a medium mixing bowl. Slowly stream in the olive oil, whisking constantly, until the dressing is emulsified. (As an alternative method, combine all ingredients in a mason jar and shake well, until the dressing is emulsified.) Set aside until ready to use.
Place the sliced kale in a large bowl, and add ¼ cup of the vinaigrette. Using your hands, mix and massage the kale and dressing together until the kale deepens in color and softens. Taste the kale, and add up to ¼ cup of additional dressing if additional flavor is needed. Gently mix in the sunflower seeds, pumpkin seeds, and strawberries, and serve immediately.