Season the 1 ½ lbs bite-size chicken thigh pieces with 1 tsp garlic powder, ½ tsp cumin, ½ tsp oregano, and salt and pepper to taste.
Heat a large skillet over medium heat (no oil needed if using a nonstick or well-seasoned skillet). Add the seasoned chicken and sauté, stirring occasionally, until the chicken is lightly browned and cooked through, about 6–8 minutes.
Add the 15 oz canned black beans (rinsed and drained), 1 ½ cups red enchilada sauce, and ½ cup salsa to the skillet. Stir to combine, bring to a gentle simmer, and cook until heated through, about 3–4 minutes.
Add the 6 small white corn tortillas (cut into 1" strips) and gently stir until the strips are fully coated in sauce and heated through, about 2–3 minutes.
Sprinkle 1 cup shredded Mexican blend cheese evenly over the skillet, cover, and cook until the cheese is melted, about 3 minutes.
Remove from heat and serve topped with sour cream, diced green onions, diced avocado, and diced tomatoes to taste.