Preheat the oven to 350 degrees. Grease a 5-inch baking dish, set aside.
Melt one tablespoon of the butter in a large skillet over medium heat, add the onions and saute until translucent, about 5 minutes, stirring occasionally. Add the zucchini and cook until slightly golden brown, stirring occasionally. Set aside.
In a small pot, add the remaining butter and melt over medium heat. Add the flour and dried spices, salt, and pepper whisk to combine, let cook one minute.
Slowly add the milk, stirring constantly to avoid lumps. Cook 5 minutes or until thickened. Remove from the heat, add the cheddar and stir until combined and smooth. Mix cheese sauce with the cooked rice, half of the parsley, and the zucchini mixture until combined. Pour into prepared baking dish.
Top with the shredded cheddar and Monterey jack blended cheese. Bake for 25-30 minutes until bubbly. Garnish with remaining parsley, optional.