Preheat the oven to 425 degrees.
In a well-seasoned, 9-inch cast iron skillet, saute the onion in the avocado oil briefly over medium heat to soften it. Add the dried tomatoes and kale. Stir the mixture and cook for another minute. Turn off the heat and cover the skillet for 5 minutes to wilt the kale (stirring occasionally).
Meanwhile, crack the eggs into a large bowl. Add the almond milk and salt. Whisk the egg mixture until it has a uniform yellow color.
Pour the eggs into the skillet with the tomato/kale mixture. Stir the mixture briefly, then sprinkle with chives. Cook on the stove over medium heat for one minute, then carefully transfer the frittata to the 425 degree oven. Bake the frittata until set (12 to 14 minutes). If you leave it in the oven too long, the frittata will be dry. Keep an eye on the center, and when it’s just set, the frittata is done.