In a large mixing bowl, whisk together olive oil, lemon juice, minced garlic, oregano, paprika, cumin, salt, and pepper.
Add chicken cubes to the marinade, tossing until evenly coated, and let sit for 10 minutes.
Heat a large non-stick skillet over medium-high heat. Add the chicken and cook, stirring occasionally, for 8 to 10 minutes or until the internal temperature reaches 165°F (74°C).
While chicken is cooking, prepare the tzatziki sauce by combining the Greek yogurt, grated cucumber, and dill in a small bowl.
To assemble, divide the cooked quinoa evenly between four serving bowls.
Top the quinoa with the cooked chicken, diced cucumber, tomatoes, and sliced red onion.
Finish each bowl with a dollop of the yogurt sauce and serve immediately.