Preheat the oven to 425 degrees F.
Spread fingerling potatoes on a large baking sheet and drizzle with olive oil and sprinkle with sea salt. Use your hands to toss everything together until the potatoes are well-coated. Wrap the garlic in foil and place on the baking sheet with the potatoes. Place potatoes and garlic in the preheated oven and bake 20 to 30 minutes, until potatoes are very soft when poked with a fork.
Remove potatoes and garlic from the oven and allow them to cool. Once cool enough to handle, peel the potatoes and chop them into bite-sized pieces. Unwrap the bulb of garlic and chop the cloves. Add the potatoes and garlic to a large mixing bowl along with the green onion.
In a small bowl, stir together the mayo, yogurt, lemon juice, lemon zest, mustard, and sea salt. Pour this dressing mixture over the potatoes and garlic and toss together.
Saute the kale leaves over medium heat in a small amount of oil until the leaves are wilted, about 2 to 3 minutes. Taste potato salad for flavor and add more sea salt and/or lemon juice to taste. Allow kale to cool then mix it in with the potato salad. Place potato salad in the refrigerator until ready to serve.