Step 1

Bring a Dutch oven filled with water to a boil over high heat. Add pasta and cook according to package directions; drain.

Step 2

Preheat oven to 350°F. Lightly coat a 9-by-13-inch baking dish with cooking spray.

Step 3

Heat 1 tablespoon oil in the Dutch oven over medium-high heat. Add onion; cook, stirring occasionally, until softened, about 3 minutes. Add bell pepper; cook, stirring occasionally, until softened, about 2 minutes. Transfer the vegetable mixture to a plate. Do not wipe the pot clean.

Step 4

Heat 1 tablespoon oil in the Dutch oven over medium-high heat. Add mushrooms; cook, stirring occasionally, until the mushrooms are browned on the edges and have released their water, 5 to 8 minutes. Return the onion and bell pepper to the pot. Stir in broth, soup, mayonnaise, Cheddar, fontina, hot sauce, 1/4 teaspoon paprika and pepper. Remove from heat; add chicken and the spaghetti, stirring until just combined. Pour the mixture into the prepared baking dish.

Step 5

Combine panko and the remaining 1 tablespoon oil and 1/4 teaspoon paprika in a small bowl. Sprinkle evenly over the casserole. Bake until bubbling on the edges, about 30 minutes. Let stand for 15 to 20 minutes before serving.