Boil the pasta until al dente, according to instructions on the package. Drain, reserving one cup of pasta water for later.
In a cast iron skillet heat the olive oil in medium high heat. Add the broccoli and cook for two minutes, until they are slightly browned yet firm. Remove the broccoli from the skillet and set aside.
To the same cast iron skillet, reduce heat to medium and add the butter. Once the butter melts, add in the flour.
Whisk the flour continuously, using a whisk for around one minute or until the flour becomes golden. Whisking continuously is extremely important to getting a smooth and creamy sauce.
Slowly stream in the in the milk while whisking to combine. Let the sauce simmer for two minutes. The sauce will thicken and coat the back of the spoon.
Add then lemon pepper and mix.
Let the sauce simmer on low heat another minute or so and then add the cheese and mix until it melts.
Stir in the boiled pasta, tuna and broccoli. Toss until the pasta and veggies are coated with the sauce. If the sauce is too thick add in some of the reserved pasta water to adjust. Taste test and adjust the seasonings at this point.
Serve hot with some fresh salad and enjoy! Store leftovers for up to three days in the refrigerator.