Preheat your oven to 375°F. Cook the whole wheat pasta according to package directions until al dente. Drain and set aside.

In a large skillet over medium heat, add a drizzle of olive oil. Sauté the diced onion until soft, about 3 minutes. Add the minced garlic and sliced mushrooms, and cook until the mushrooms begin to soften, about 3–4 minutes.

Sprinkle the flour over the sautéed vegetables and stir to coat. Gradually whisk in the milk and chicken broth, stirring continuously until the mixture thickens. Stir in the dried thyme, dried oregano, and season with salt and pepper to taste.

Remove the skillet from the heat and stir in the plain Greek yogurt and half of the shredded white cheddar cheese. Gently fold in the drained tuna, frozen peas, and cooked pasta until everything is well combined.

Transfer the mixture to a greased 9x13-inch baking dish. Sprinkle the remaining white cheddar cheese evenly over the top, then add the whole wheat breadcrumbs as a final layer.

Bake in the preheated oven for 20–25 minutes, or until the casserole is bubbly and the breadcrumb topping is lightly golden.