Warm a large skillet over medium-high heat. Toast each tortilla for about 30–60 seconds per side (dry, no oil) until the edges show light color. Stack and cover them with foil (or invert a bowl) so they stay pliable.
In the same skillet, reduce heat to medium, add ½ Tbsp oil, and cook chicken breasts about 5–7 minutes per side until fully cooked (165 °F internal). Let rest, then chop or shred into bite-size pieces.
Purée both cans of diced green chiles (with juices) in a blender. In a small pot, heat oil, whisk in flour, cumin, garlic powder, onion powder; cook until it simmers and bubbles for about 1 minute. Then stir in water and the puréed chiles, whisk until smooth, let it simmer briefly, and season with salt.
Preheat the oven to 350 °F. In a bowl, combine sour cream, half the shredded cheese, green onions, garlic powder, cumin, cayenne, salt, and the chopped chicken. Stir well to combine.
Place about ¼ cup of filling in each tortilla, roll it closed, and lay seam-side down in the casserole dish. Pour the green chile sauce evenly over all the rolled enchiladas. Top with the remaining shredded cheese. Bake for 30 minutes until sauce is bubbling and cheese is melted.
Allow to rest for a few minutes after baking. Serve warm, garnish, and enjoy.