Tuna Noodle Casserole

8 oz penne pasta
2 Tbsp olive oil
¼ lb shiitake mushrooms, chopped
1 - 2 cloves garlic, minced
2 - 3 cups spinach, large stems removed, roughly chopped
2 cups red bell peppers, chopped (a mix of colored bell peppers is a nice substitute too, if only for the added bit of color)
3 - 4 (5 oz) cans albacore tuna in water, drained and flaked
2 cups milk
½ cup Greek yogurt
2 Tbsp whole wheat flour
3 Tbsp mustard
2 tsp fresh basil,
2 tsp fresh thyme
½ tsp cayenne pepper
small pinch fine-grain sea salt + more to taste
pinch freshly ground black pepper + more to taste
½ cup (2 oz) grated Parmigiano-Reggiano cheese, divided
2 cups frozen veggie mix
¼ - ½ cup Panko breadcrumbs

Preheat oven to 325° F
Cook the noodles until al dente (according to the directions on the package)
In a large skillet over medium heat, warm the olive oil. Add mushrooms, and cook 2 or 3 minutes, until they're beginning to release their liquid.
Add garlic and bell peppers, cook 3 or 4 minutes more.
Add the spinach and continue to sauté, stirring occasionally, allowing it to wilt
Make the sauce:
Measure the spices ahead of time and set aside
In a medium-sized pot over medium heat, add the milk. Stir constantly, until it's on the verge of boiling.
Add Greek yogurt, flour, mustard, basil, thyme, cayenne, salt and pepper, all while continuing to stir
Add ¼ Parmesan cheese and remove from heat, continuing to stir until the cheese has melted. (the sauce should be thick)
Combine the noodles, tuna, sauce, frozen veggies, cooked mushrooms and spinach
Transfer to a shallow baking dish, top with the remaining Parmesan cheese, and breadcrumbs.
Bake for 10-15 minutes until the casserole is golden and bubbly.