Preheat your grill or grill pan over medium-high heat. Season the chicken breasts with salt, black pepper, and olive oil. Grill the chicken for about 6-7 minutes per side, or until the internal temperature reaches 165°F. Remove from the grill and let it rest for 5 minutes before slicing.
While the chicken is grilling, prepare the chimichurri sauce. In a bowl, combine the parsley, cilantro, garlic, red pepper flakes, red wine vinegar, and olive oil. Mix well and season with salt and pepper to taste. Set aside.
For the garlic sauce, mix together the Greek yogurt, mayonnaise, minced garlic, lemon juice, and a pinch of salt and pepper in a separate bowl. Adjust seasoning to taste and set aside.
To assemble the bowls, divide the cooked brown rice among four bowls. Top each bowl with sliced grilled chicken, cherry tomatoes, avocado, corn, and mixed greens.
Drizzle the chimichurri sauce generously over the chicken and finish with a dollop of garlic sauce on top.
Serve immediately and enjoy!