Prepare the cream sauce by adding all the ingredients to a blender, and blending until very smooth and creamy. Set aside.
Make "breadcrumbs" by adding the nuts, seeds, and salt to a blender, and pulsing until a course flour is formed. Set aside.
Boil pasta. If baking this as a casserole, preheat the oven to 425 degrees F.
Once the pasta is cooked (slightly undercook, since it will continue to cook in the casserole), add the cream sauce, peas, and tuna, and heat over medium high heat. Stir the sauce into the mixture until the sauce begins to bubble and thicken from the arrowroot.
Season with fresh thyme, sea salt and black pepper.
This pasta is the creamiest if eaten straight from the stovetop. The sauce absorbs into the pasta as it bakes. Stop at this stage if you'd like to serve dinner quickly!
Add the pasta to a casserole dish, and top with nut and seed "breadcrumbs", for a salty crunchy topping.
Bake for about 10 minutes uncovered, until the topping begins to brown and get crunchy. Serve immediately.