For the Casserole:

• 10 ounces dry pasta shells (or rotini, fusilli, or your preferred pasta)
• 3 tablespoons butter, divided
• 1 white onion, diced
• 8 ounces baby bella mushrooms, sliced
• 1 teaspoon dried thyme
• Salt and pepper, to taste
• 1/4 cup all-purpose flour (or whole wheat flour or gluten-free flour)
• 1 3/4 cups unsweetened almond milk (or cashew milk or regular milk)
• 1/2 teaspoon garlic powder
• 1/2 cup grated parmesan cheese
• 2 (5-ounce) cans tuna, drained
• 1 cup frozen peas
• Salt and pepper, to taste

For the Topping:

• 1/2 cup breadcrumbs (gluten-free if desired)
• 1 tablespoon butter, melted