In a small glass bowl, whisk together the olive oil, lemon juice, lemon zest, minced garlic, dried oregano, sea salt, and black pepper to create the marinade.
Place the chicken breast in a shallow dish and pour half of the marinade over it, ensuring it is well coated.
In a separate container, toss the trimmed asparagus spears with the remaining half of the marinade.
Preheat a grill or cast-iron grill pan over medium-high heat until it is hot and lightly smoking.
Place the chicken on the grill and cook for approximately 6 to 7 minutes per side, or until the internal temperature reaches 165°F.
During the last 5 minutes of the chicken's cooking time, add the asparagus to the grill and cook until tender-crisp with light char marks.
Slice the chicken into strips and serve alongside the grilled asparagus over a bed of warmed quinoa.