Preheat the oven to 375 degrees Fahrenheit.
In a large skillet, heat the vegetable oil over medium-high heat until it shimmers.
Add the onions and green pepper to the skillet and cook for 4 minutes or until softened, stirring occasionally.
Stir in the garlic and cook for an additional minute before removing from the heat.
In a medium saucepan, whisk together the flour and water until smooth.
Gradually add the half and half, stirring constantly over medium-high heat until thickened (about 5 minutes).
Add all of the cheeses to the saucepan and stir until completely melted.
Stir in salt, lemon pepper, sugar, yellow mustard, white vinegar and Tabasco sauce.
In a large pot of boiling salted water, cook the macaroni according to package instructions until just al dente.
Drain the macaroni and return it to the pot.
Pour the cheese sauce over the macaroni and stir to combine.
Add the cooked vegetables to the macaroni and cheese and stir until completely incorporated.
Pour the macaroni and cheese mixture into a 9x13 baking dish and top with the remaining 8 ounces of shredded cheddar cheese and 2 tablespoons of Pecorino Romano cheese.
Bake in a preheated oven for 25 minutes or until bubbly and golden brown on top.
Let cool for 10 minutes before serving.