In a medium sized mixing bowl add the shredded cheese, cornstarch, garlic powder, paprika, cumin, red chili flakes, kosher salt, and cayenne pepper. Using a wooden spoon or your hands toss the cheese with the spices. Make sure that the spices are fully mixed throughout the cheese and no spices remain on the bottom of the mixing bowl. 

In a medium sized saucepan over medium heat melt the butter. Once the butter has melted add the scallions and sautee for 1 minute until they start to soften.

Add in the tomatoes and cook, stirring regularly until slightly thickened, about 2-3 minutes. 

Reduce the heat to medium-low and add in the evaporated milk and cheese. Stir regularly and heat until thickened, but not boiling, this should take about 5 minutes. 

Once thickened, remove from heat and add a small amount of extra milk or water to get the desired consistency, I typically add around 3-4 tablespoons. (Adding milk after the initial cooking time makes the sauce creamy and silky smooth.)

Serve immediately or let cool to room temperature. Store cheese dip in an airtight container and refrigerate.