1. In a bowl, mix red onion slices and lime juice.
2. Break trout into flakes.
3. Cut cream cheese into 1/2-inch chunks.
4. Mix enchilada sauce and chicken broth and pour 1 cup of the mixture into a shallow 3-quart (9- by 13-in.) casserole.
5. Stack tortillas and put in a microwave-safe plastic bag but do not seal. Heat in a microwave oven on full power (100%) just until hot, 1 to 2 minutes.
6. Dip tortillas, 1 at a time, in sauce in casserole and turn over to coat. Stack at 1 end of the casserole. Scatter 1/8 of the trout, cream cheese, and green onions across center of 1 tortilla. Roll to enclose filling and set, seam down, in sauce. Repeat to fill remaining tortillas, pushing unfilled ones to the end of the casserole as you work.
7. Pour remaining enchilada sauce mixture over and around filled tortillas.
8. Bake in a 400° oven until sauce bubbles, 10 to 12 minutes (about 9 minutes in a convection oven). Sprinkle jack cheese over enchiladas and bake until melted, 2 to 3 minutes more.
9. With a slotted spoon, lift the red onion slices from bowl and scatter over the enchiladas. Serve with a wide spatula. Season to taste with lime juice from the bowl.