Preheat your oven to 350°F and lightly spray a 2-quart baking dish with cooking oil spray. Set aside.

To steam the broccoli, add the broccoli florets to a steaming basket and place it over a pot with boiling water. Cover and steam until just tender. Transfer the steamed broccoli to the prepared casserole dish and set aside.

Meanwhile, heat oil in a large pan over medium heat. Add onions and sauté until translucent, about 3-4 minutes. Stir in the garlic, mushrooms, and smoked paprika and continue to cook for 5-6 minutes.

In a small pot over medium heat, whisk together milk, cornstarch, salt, and pepper until it starts to thicken, about 2-3 minutes.

Transfer the onion mushroom mix to the casserole and pour over the milk sauce.

Clean the pan with a paper towel, lightly spray with cooking oil spray, and stir the breadcrumbs over medium heat until golden, then sprinkle over the casserole.

Place the casserole into the preheated oven and bake for about 30 minutes.