Combine the taco seasoning: in a small bowl mix 1 teaspoon garlic powder, 1 teaspoon cumin, 1 teaspoon kosher salt, 1/2 teaspoon chili powder, 1/2 teaspoon paprika and 1/2 teaspoon oregano. Set aside.
Dice the red onion. Reserve 3 tablespoons of the diced onion for the pico de gallo and keep the remaining diced onion for cooking.
Make the pico de gallo: in a small bowl combine the reserved 3 tablespoons diced onion, 1 roma tomato (cored and diced), 1/4 cup minced cilantro and the juice from one lime half. Season with kosher salt to taste and set aside.
Cut the chicken breasts into 1/2-inch cubes so you have 1 1/4 pounds total.
Heat 2 teaspoons olive oil in a large skillet over medium-high heat. Add the cubed chicken and cook, stirring occasionally, until the chicken is browned and cooked through, about 4–6 minutes.
Add the remaining diced onion, the diced poblano pepper, and the prepared taco seasoning to the skillet. Cook, stirring, until the vegetables soften and everything is well combined and the chicken is fully cooked, about 2–4 minutes.
Stir in 1 cup frozen or fresh corn kernels and cook just until the corn is heated through, about 1–2 minutes. Remove the skillet from the heat.
Reheat the 3 cups cooked brown rice if necessary. Divide the rice among 4 bowls.
Top each bowl of rice with the chicken–poblano–corn mixture. Sprinkle the 1/4 cup cheddar‑jack cheese evenly over the bowls.
Add 1/4 cup 2% sour cream or Greek yogurt if using, spoon the pico de gallo on top, and garnish with additional minced cilantro. Squeeze the remaining lime half over the bowls if desired.