Rinse the quinoa under cold water and then combine it with 2 cups of water in a large pot. Bring to a boil over medium-high heat.
Once boiling, reduce the heat to low, cover, and simmer for about 15 minutes or until the quinoa is cooked and water is absorbed. Remove from heat and let sit, covered, for an additional 5 minutes. Fluff with a fork.
While the quinoa is cooking, prepare the dressing. In a small mixing bowl, whisk together tahini, lemon juice, olive oil, minced garlic, salt, and pepper. If the mixture is too thick, add a tablespoon of water at a time until desired consistency is reached.
In a large bowl, combine the cooked quinoa, chickpeas, chopped bell pepper, halved cherry tomatoes, diced cucumber, and spinach. Toss gently to mix.
Drizzle the dressing over the quinoa mixture and toss to combine evenly.
Serve the power bowl topped with sliced avocado and garnish with fresh parsley or cilantro if desired.