Bring 1 1/3 cups water and quinoa to a boil in a saucepan. Reduce heat to medium-low, cover, and simmer until quinoa tender and water absorbed, 15 to 20 minutes. Set aside to cool.

Place a steamer basket into a saucepan with 1 inch water; bring water to a boil. Add kale, cover, and steam 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 emulsified; pour over salad.