In a small bowl, whisk together the olive oil, lemon juice, lemon zest, oregano, garlic powder, sea salt, and black pepper to create the marinade.
Place the chicken breast in a shallow dish or resealable bag and pour half of the marinade over it, ensuring it is well coated. Let it marinate for at least 15 minutes.
Preheat your grill or grill pan over medium-high heat.
Place the marinated chicken on the grill and cook for 6 to 7 minutes per side, or until the internal temperature reaches 165°F.
While the chicken is cooking, toss the asparagus spears with the remaining marinade.
Add the asparagus to the grill during the last 4 minutes of the chicken's cooking time, turning occasionally until they are tender-crisp and lightly charred.
Remove the chicken and asparagus from the grill and let the chicken rest for 3 minutes before slicing.
Serve the sliced chicken and grilled asparagus over a bed of warm cooked quinoa.