Mix all the spices (chili powder through pepper) in a small bowl.
Add pepper and onion strips to a large ziploc bag (or a large bowl). Add olive oil and half of the spice mix to the bag or bowl and mix well.
Over medium heat in a grill pan or frying pan, cook the peppers and onions until desired tenderness (or in a veggie basket on grill)
Cut the beef into thin strips about 4-5 inches long by 2 inches wide. Rub both sides of the beef strips with the remaining spice mix.
Roll the onions and peppers into the beef strips and secure with toothpicks.
Cook them until all sides are browned in the same grill pan or on the grill (about 2 minutes each side).
Queso
In a medium sauce pan over medium heat, melt butter. Add flour, and whisk until smooth. Slowly add milk. Whisk until smooth and bubbly. Stir in cheese, and stir until melted and smooth.
Add Rotel. Mix to combine. Add salt and pepper to taste.
Notes
NOTE: You can also just do 7 ounces of diced tomatoes and 3 ounces of canned green chiles if you can't find Rotel.