Preheat oven to 375°F (190°C). Lightly grease a 9x9-inch baking dish or similar casserole dish.
Cook the pasta according to package instructions until al dente. Drain and set aside.
Make the roux: In a medium saucepan over medium heat, whisk the flour and milk together until smooth and slightly thickened, about 3–4 minutes.
Add cheese & seasonings: A Reduce heat to low. Stir in Greek yogurt, cheddar, mozzarella, Dijon mustard, garlic powder, onion powder, salt, and pepper. Mix until cheese is melted and sauce is smooth. If using cauliflower puree, stir it in here.
Combine with pasta: Pour the sauce over the cooked pasta and mix well to coat evenly.
Transfer to baking dish: Spoon the mixture into your prepared baking dish and spread it out evenly.
Make the topping: Mix the breadcrumbs with olive oil or melted butter. Sprinkle evenly over the top of the pasta.
Bake uncovered for 20–25 minutes, until the top is golden and bubbly.
Cool slightly before serving for best texture and flavor.