In a medium bowl, whisk together the olive oil, minced garlic, lemon zest, lemon juice, dried oregano, thyme, smoked paprika, salt, black pepper, and optional red pepper flakes. Pat the chicken breasts dry with paper towels, then place them in a shallow dish or zip-top bag. Pour the marinade over the chicken, ensuring it's coated evenly, cover it, and refrigerate for at least 30 minutes—ideally 1-2 hours for maximum flavor.

Rinse the brown rice or quinoa under cold water until the water runs clear. In a saucepan, combine the rinsed grains, chicken broth or water, and ½ teaspoon of salt. Bring the mixture to a boil, then reduce the heat to low, cover, and simmer: 35-40 minutes for brown rice, 15 minutes for quinoa, or 20-25 minutes for a mixture. Once cooked, remove from heat and keep covered for about 5-10 minutes to steam, then fluff with a fork.

Preheat your oven to 400°F (200°C). On a baking sheet, arrange the broccoli, red bell pepper, yellow bell pepper, and red onion. Drizzle with olive oil and sprinkle with salt, black pepper, garlic powder, and Italian seasoning. Toss the vegetables well to coat them evenly. Roast for 18-22 minutes, tossing halfway through, until the veggies are tender and have nice charred edges.

Heat a large skillet or grill pan over medium-high heat. Remove the marinated chicken from the refrigerator and cook for 5-7 minutes on one side. Flip the chicken and continue cooking for another 5-7 minutes until the internal temperature reaches 165°F (74°C) and the chicken is golden brown. Alternatively, place the marinated chicken on a baking sheet and bake in the preheated oven for 18-25 minutes until it reaches the same safe temperature.

After cooking, let the chicken rest for 5-10 minutes. This allows the juices to redistribute for maximum tenderness. Slice the chicken against the grain into strips or bite-sized pieces and spoon any collected juices over the top for extra flavor.

Divide the cooked grains evenly among 4-5 containers, aiming for ¾ to 1 cup each. Top each container with an equal portion of the roasted vegetables and the sliced chicken. Garnish generously with fresh parsley, optional dill or cilantro, and a lemon wedge for brightness. If desired, store toppings like feta or avocado separately until ready to eat.

Allow the meal prep bowls to cool to room temperature (under 1 hour) before sealing them. Refrigerate the bowls for up to 4 days. When you're ready to enjoy, remove the lemon wedges, then microwave for 1.5-3 minutes, stirring halfway. Squeeze fresh lemon juice over your meal and add any toppings back before serving.