01 - Preheat the oven to 400°F and line a baking sheet with parchment paper.
02 - Whisk together olive oil, lemon juice, Dijon mustard, garlic, smoked paprika, oregano, salt, and black pepper in a bowl.
03 - Place chicken breasts in a shallow dish and pour half of the marinade over them, turning to coat evenly. Let rest for 10 minutes.
04 - Toss broccoli, cherry tomatoes, and sliced red bell pepper with the remaining marinade. Arrange vegetables evenly on the prepared baking sheet.
05 - Nestle marinated chicken breasts among the vegetables on the baking sheet. Roast for 25-30 minutes until chicken reaches an internal temperature of 165°F and vegetables are tender.
06 - While roasting, rinse quinoa under cold water. Combine quinoa, 2 cups water, and a pinch of salt in a saucepan. Bring to a boil, then cover and reduce heat to a simmer for 15 minutes or until water is absorbed. Fluff with a fork.
07 - Divide baby spinach and cooked quinoa evenly among 4 bowls. Top with roasted vegetables and sliced chicken breasts. Garnish with crumbled feta cheese and chopped parsley.