Heat the oven to 350 °F. Have the oven fully hot before assembling the casserole so the cheese begins melting evenly once the dish goes in.

Grease a 9x13 baking dish and arrange the halved tortilla pieces across the bottom. Cover the base as evenly as possible to create a sturdy layer beneath the creamy filling.

Melt the butter in a skillet over medium heat. Let it melt completely without browning before adding the vegetables.

Cook the chopped onion and red bell pepper in the butter until tender. The vegetables should soften and smell sweet, with no firm crunch remaining.

Stir the heavy whipping cream and chicken broth into the skillet and bring the mixture to a gentle simmer. Keep the heat moderate until the sauce thickens and bubbles softly around the edges.

Season the sauce with the chicken bouillon powder and salt and pepper to taste, then stir in the drained RoTel tomatoes. The sauce should look creamy and cohesive, not thin or watery.

Fold in the shredded chicken and chopped green onions. Turn until the chicken is evenly coated with the warm sauce.

Spoon the chicken mixture over the tortilla layer and scatter the Colby Jack cheese over the top. Spread the filling into an even layer so the cheese melts consistently.

Bake for 25-30 minutes. The casserole is ready when the cheese is melted and the sauce is gently bubbling at the dish edges.

Rest the casserole for 10 minutes before serving. This pause allows the creamy layers to settle for cleaner slices.