Heat oil over medium-high heat in a large skillet. Add chorizo to the skillet and cook until browned on the outside. Set aside on a paper towel-lined plate.
Turn the heat down to medium. Add the diced onion, jalapeños with seeds and ground cumin. Cook until softened, about three to four minutes. Remove from heat.
In the large pan with deep sides, add the cubed cheese. Top with the browned chorizo, onion, jalapeños and Rotel tomatoes. (A disposable aluminum pan works great.)
Place in the 225-degree smoker and smoke for an hour and a half to two hours, stirring the cheese mixture every 30 minutes.
Remove from the smoker once the cheese has fully melted. Stir in the evaporated milk. Serve with tortillas chips and your favorite toppings.