Season the chicken by drizzling with about 1 tablespoon olive oil, garlic, Greek seasoning, and lemon zest and juice. Allow marinating for about 20-30 minutes or up to overnight. Heat a saute pan over medium-high heat and cook the chicken for about 3-4 minutes per side, until lightly browned and cooked through. Remove from pan and set aside. Add another drizzle of olive oil and saute the onion and peppers for 2-3 minutes. Vegetables should be caramelized, but still crisp. While vegetables are cooking, dice the chicken into cubes and add back to the pan. Season to taste with salt and pepper.
To make the Tomato Cucumber Salad, combine all ingredients in a medium bowl and season with salt and pepper.
To build the Greek Chicken Bowls, spoon about 1/2 cup of cooked grain into a large bowl. Add a generous scoop of the chicken and vegetables, followed by a scoop of the Tomato Cucumber salad. Garnish with sliced olives and additional dill, if desired.