Bring the quinoa and 1 1/3 cup water to a boil in a saucepan. Reduce heat to medium-low, cover, and simmer until the quinoa is tender, and the water has been absorbed, about 15 to 20 minutes. Set aside to cool.
Place kale in a steamer basket over 1 inch of boiling water in a saucepan. Cover saucepan with a lid and steam kale until hot, about 45 seconds; transfer to a large plate. Top kale with quinoa, avocado, cucumber, bell pepper, red onion, and feta cheese.
Whisk olive oil, lemon juice, Dijon mustard, sea salt, and black pepper together in a bowl until the oil emulsifies into the dressing; pour over the salad.