Preheat your oven to 350.
In a blender add spinach and milk. Puree until smooth with no visible spinach floaters.
Cook your pasta to al dente, drain and add a little butter to prevent sticking. Set aside.
Start your roux by adding butter to saucepan over medium high heat. Once butter melts add flour and mix well. Allow flour to cook out for about a minute or two. With a whisk in one hand slowly pour in a little of your green milk whisking well. Once it starts to thicken add the rest of your milk and turn the heat up. Keep whisking until the mixture is bubbling and thickened to ensure the milk does not burn in the pot. Turn heat down to simmer and mix in taco seasoning. Next in handfuls add in 2.5 cups of cheese stirring after each addition until all cheese is gone. Add salt & pepper to taste. Remove from heat.
Pour sauce and noodles into lightly greased 8x8 or 9x9 baking dish. Add broccoli and mix well to combine. Top with remaining 1/2 cup cheese.
Place in oven uncovered for about 15-20 minutes or until bubbly and cheese is starting to brown.