Thinly slice the onion. Place the slices into a mason jar or heavy duty plastic container.
Bring the water, vinegar, sugar and salt to a boil in a small saucepan. Once the salt and sugar are dissolved, pour the pickling liquid over the onions. Fill to the top of the container and seal it.
Let it sit until it cools to room temperature. Store in the refrigerator.
Make the Chicken
Combine all marinade ingredients in a large bowl and mix well. Cut chicken breast into bite-sized cubes and toss in the marinade. Cover with plastic wrap and refrigerate at least 30 minutes, up to overnight.
Preheat oven to 375 degrees. Spread chicken onto an ungreased baking sheet. Bake for 20 minutes. Set aside.
Make the Harissa Vinaigrette
Whisk all ingredients except for the olive oil in a small bowl. Slowly pour the olive oil into the mixture, whisking constantly.
Make the Basmati Rice
Bring one cup of water to a boil in a small saucepan. Stir in the rice. Reduce the heat to low. Cover. Cook 15-20 minutes. Fluff with a fork.
Assemble the Bowls
Divide the greens among 4 serving bowls. Top with cooked rice, chicken, cubed feta cheese, hummus, roasted corn, diced avocado, sliced cucumbers and pickled onions. Drizzle with harissa vinaigrette.