Method

1. Steam or microwave cauliflower until tender. Drain of any excess water and set aside.
2. Heat butter in a pan over medium heat. Add onion and cook for 3 minutes, then add garlic and cook another 30 seconds. 
3. Sprinkle flour over the onions and stir for 1 minute. Slowly whisk in the milk, stirring constantly to prevent lumps. Simmer until slightly thickened (3–5 minutes). 
4. Stir in Dijon mustard, cheese, peas, and cooked cauliflower.
5. Gently fold in tuna. Season with salt and pepper to taste. 
6. Pour mixture into a baking dish.  
7. Sprinkle with Parmesan on top.  
8. Bake at 180°C for 15–20 minutes until bubbling and golden on top. 
9. Serve with steamed vegetables or salad