Add the sliced chicken to a non-reactive bowl. Add olive oil, Dijon mustard, lemon juice and zest, grated garlic, dried oregano, red pepper flakes (if using), salt, and pepper. Mix well and let marinate for 15-30 minutes while prepping the grains.

In a medium pan, combine rinsed quinoa, rinsed lentils, and chicken broth. Bring to a boil, then reduce heat to a simmer, cover, and cook for 20 minutes or until broth is mostly absorbed. Let sit covered for 15 minutes, then fluff with a fork.

In a large bowl, combine chopped cherry tomatoes, chopped Persian cucumbers, chopped roasted red peppers, chopped black olives, minced shallot, chopped parsley, chopped mint, chopped dill, lemon juice, garlic powder, salt, and pepper. Toss well to mix and adjust seasoning if needed.

Heat a large skillet over medium-high heat. Add marinated chicken in a single layer and cook for about 3-4 minutes per side until cooked through (internal temperature should reach 165°F/74°C). Remove from skillet and set aside.

Layer cooked quinoa and lentils in a bowl. Top with Mediterranean salsa, sliced chicken, and a handful of lettuce. Add any other desired toppings such as avocado or feta cheese.