Slice the chicken breast into bite-sized pieces and toss in a bowl with the first lemon juice measurement, oregano, garlic powder, cumin, salt, and pepper.
Heat olive oil in a large skillet over medium-high heat and sauté the chicken until golden brown and cooked through, about 6-8 minutes.
In a separate pan, lightly sauté the cauliflower rice for 3-4 minutes until tender, then stir in the cooked quinoa to warm through.
Prepare the dressing by whisking together the tahini, second lemon juice measurement, and water in a small bowl until smooth and creamy.
Assemble the bowls by placing the cauliflower-quinoa mixture at the base and topping with the cooked chicken, diced cucumber, halved cherry tomatoes, and minced red onion.
Garnish with fresh chopped parsley and drizzle the lemon-tahini sauce over the top before serving.