In a small bowl, whisk together the olive oil, lemon juice, minced garlic, 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 evenly coated on both sides.
In a separate bowl, toss the trimmed asparagus spears with the remaining half of the marinade.
Preheat a grill or a heavy-bottomed grill pan over medium-high heat until it is hot.
Place the chicken on the grill and cook for 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 and lightly charred.
Remove everything from the heat and serve the chicken and asparagus over a bed of warm, fluffy quinoa.