Cook noodles by following the instructions on the package.
While the noodles are cooking, steam the chopped broccoli and cauliflower until tender.
Once the noodles are cooked and the vegetables are steamed, combine the two in a large dutch oven (or relatively similar, oven safe dish) and add in the peas, spinach, tuna, dill, parmesan and 1 cup of the cheddar cheese. Mix well and place aside.
Next, preheat the oven to 350° F
Preparing the Cream Sauce
In a large saucepan, on medium to high, heat oil and add onions. Cook until soft.
Add the garlic and mushrooms to the saucepan. Cook until the liquid from the mushrooms has evaporated, 5-7 minutes.
Add flour and cook for 3 minutes, then whisk in chicken stock and let thicken.
Add milk, cream cheese, salt, pepper and thyme. Let simmer for 5 minutes, or until thick.
Pour the cream sauce over the mixture in the dutch oven and mix.
Cover the mixture with the remaining 2 cups of cheddar cheese.
Place in the oven, with a lid on and bake for 30 minutes or until very bubbly.