Pour in the water, and season with chili powder, 1/2 teaspoon salt, cumin, 1/4 teaspoon black pepper, garlic powder, onion powder, and cayenne pepper.
Bring to a simmer over high heat, then reduce heat to medium-low, and simmer 15 minutes. After 15 minutes, stir in 4 ounces of green chiles, onion, and garlic; continue simmering until the liquid has reduced to 1 cup.
Reserve remaining 3 ounces of chopped green chilies. Remove the chicken, shred with two forks, and return to the onion mixture.
Meanwhile, melt the butter in a small saucepan over medium heat. Stir in the flour, and cook for 1 minute. Whisk in the water and bouillon cube until the water has thickened and the bouillon cube has dissolved, about 4 minutes. Whisk in reserved 3 ounces of green chilies and the sour cream; season to taste with salt and pepper. Keep warm.
Spray an 8 x 8 baking dish with cooking spray.
Place a tortilla onto your work surface, then spoon about 1/3 cup of the chicken filling halfway between the bottom edge and the center of the tortilla.
Flatten the filling into rectangle shape with the back of a spoon. Sprinkle about 1 ounce of the Monterey Jack cheese over the filling.
Fold the bottom of the tortilla snugly over the filling, then fold in the left and right edges. Roll the chimichanga up to the top edge, forming a tight cylinder.
Place rolled chimichanga, edge side down, in baking dish. Repeat with the remaining ingredients.
Lightly brush chimichangas with canola oil. Bake in preheated oven for 15 to 20 minutes, until brown.