Preheat your oven to 400 degrees f. and grease/brush/spray an ovenproof dish (10-cup capacity, I used 9x9) with a bit of avocado, or olive oil.
In a heavy saucepan, heat 1 Tablespoon of oil over medium-high heat.
Add in onions, celery and carrot, cook stirring constantly for 5 minutes until slightly softened.
Add in zucchini and beans, and continue cooking for a few more minutes or until vegetables are crisp tender.
Once the veggies are crisp tender and caramelized a bit, then transfer to a bowl and set aside.
In the same skillet over medium low heat, melt your ghee/butter and add in flour. Whisk quickly until combined.
Slowly add in the milk and continue whisking until the mixture is well combined.
Whisking occasionally, allow to simmer on low until the sauce thickens.
Once you have a thick, creamy sauce immediately add in your cooked vegetables, the tuna and half of the parmesan cheese.
Season with a touch of sea salt and pepper to your taste.
Stir to combine this mixture really well.
Spoon your cooked brown rice into the prepared baking dish, top with fresh spinach and tuna-veggie mixture as shown in the pictures.
Sprinkle the remaining parmesan on top and bake for 20-25 minutes, until bubbly and golden brown.
Serve warm with salad leaves and squeeze fresh lemon juice on top.
Enjoy!