Preheat the oven to 350°F. Heat 2 tbsp olive oil in a pan over medium heat, then sauté 2 oz onions and 1 tbsp garlic for 2 minutes.
Add 12 oz salmon and stir to cook for 2 minutes.
Add 8 oz mushrooms and stir to cook for another minute.
Add 2 oz carrots, 1 1/2 tsp Cajun, 1/2 tsp paprika, 1/2 tsp garlic powder, 1/2 tsp pepper, and 1/2 tsp salt, and stir to cook for 2 minutes. Remove from heat.
Transfer the fish filling to a large mixing bowl along with 10 oz al-dente fusilli, 1 cup milk, 1/4 cup heavy cream, 2 tbsp all-purpose flour, 1 oz cheddar, and 4 oz green peas. Mix well, then transfer all to a baking dish.
Mix 1/3 cup plain panko with 1 tbsp melted, unsalted butter, then sprinkle this mixture on top of the pasta.
Place the baking tray on the lower rack of the oven and bake for 10 minutes. Then, move it to the top rack and bake for another 10 minutes.
Sprinkle 2 tbsp chopped parsley on top and enjoy.