Cut the chicken into 1/2-inch cubes and set aside.
Mix the taco seasoning: combine garlic powder, cumin, 1 teaspoon kosher salt, chili powder, paprika, and oregano in a small bowl; set aside.
Make the pico de gallo: reserve 3 tablespoons of the diced onion, then combine the reserved onion, diced tomato, 1/4 cup minced cilantro, 2 teaspoons lime juice (from the halved lime), and 1/4 teaspoon kosher salt in a bowl; stir and set aside.
Heat 2 teaspoons olive oil in a large skillet over medium-high heat. When hot, add the chicken and cook, stirring occasionally, until it begins to brown, about 2 to 3 minutes.
Add the remaining diced onion, diced poblano, and the prepared taco seasoning to the skillet; cook until the vegetables soften, about 2 to 3 minutes.
Stir in 1/2 cup water and the corn kernels; cook 1 to 2 minutes more until heated through, then remove the skillet from the heat.
Divide 3 cups of hot cooked brown rice among 4 bowls. Top each with the chicken and vegetable mixture, sprinkle with 1/4 cup cheddar-jack cheese, add pico de gallo, and dollop with sour cream or Greek yogurt if using; garnish with additional cilantro.
