Combine oregano, lemon juice, garlic, and olive oil and whisk until well combined. {I actually just shake it in a jar}
Reserve 1/4 cup of marinade. Pour the remaining marinade over the chicken breasts and marinate for 30 minutes.
Heat 2 tsp of olive oil in a pan over medium heat. Cook chicken for 4-5 minutes on each side or until fully cooked.
Preheat the oven to 400 degrees. Toss grape tomatoes with 1 tsp of olive oil and place on a baking sheet. Roast in the oven for 10 minutes.
In a large bowl, combine the quinoa, baby spinach and tomatoes. Toss well and pour marinade over salad mixture. Add to plates and top with sliced, cooked chicken.