Heat 2 tablespoons of the oil in a large saute pan over medium heat.
Add onion and pepper, season with salt and pepper, and cook 10 minutes.
Increase heat to medium high and add the sausage. Cook 3-5 minutes or until the mixture turns golden in color.
Add the chiles, stir, and reduce heat to low to keep warm.
Combine the cheese, cornstarch and Cajun seasoning in a large bowl.
Heat the remaining 1 tablespoon of oil in a pot over medium heat.
Add the garlic and cook for 1 minute.
Add the beer (or broth) and bring to a simmer.
Reduce heat to low. Working in batches, add some of the cheese and whisk until melted.
Spread chips out onto a large platter.
Top with the cheese sauce, then the sausage mixture.
Garnish with tomatoes, green onions, and sour cream.