Preheat oven to 350 degrees.
Heat the olive oil in a pot over medium heat.
Whisk in the flour, until it is clump free. Add in the garlic and stir. Add ½ cup of the vegetable broth and whisk until smooth. Slowly add in the remaining vegetable broth. Add the tuna, and bring to a low boil.
Once boiling, add the spinach, reduce the heat to low, and simmer. Turn off heat when sauce reaches a creamy thick texture.
Add in the pasta and stir until pasta is coated with the sauce.
Add the pasta to a skillet or baking pan. Sprinkle with GF breadcrumbs.
Place in oven for 30 minutes to crisp the top. Remove when top of casserole is golden.
Cool for 10 minutes then serve!