
Heat the olive oil in a 10-inch cast iron skillet over medium heat. Add the garlic and onion and saute one minute.
Add the kale, reduce the heat to medium-low and stir for another 3-4 minutes, or until the kale has become soft and wilted.
While the kale is wilting, add the eggs and yogurt to a large mixing bowl and whisk until creamy. Season the egg mixture with salt and pepper.
Reduce the heat to low, add the cubed butternut squash to the pan and stir with the kale and onions.
Pour the egg mixture into the skillet and sprinkle the goat cheese on top. Cook for 8-10 minutes, or until the sides are just starting to set.
Turn the top oven broiler on. Transfer the frittata to the oven (on a middle shelf) and continue cooking for another 8 to 10 minutes, checking every few minutes to ensure the top isn't browning too much. If it is, you can lower the rack in your oven.
Remove the frittata from the oven, slice and serve.