Sauté shrimp shells in a tablespoon of vegetable oil on medium high heat for 2 minutes. Add enough water to cover shells and reduce heat. Simmer for 30 minutes. Strain liquid and discard shells.
Pour liquid into a measuring pitcher. Add hot water to obtain 2 qt. Whisk in soup base and continue whisking for 1 minute. Let mixture stand for 3-5 minutes and then whisk again vigorously.
Add1 lb. queso blanco and stir until melted. Stir in sautéed onions. Set aside and cool.
Sauté shrimp in a large skillet with 2 tbsp. of butter; set aside. Remove pan from heat and add Grand Marnier. Return to heat and ignite to burn off the alcohol. Add liquid to soup base mixture and stir to incorporate.
Grill peppers over open flame until completely charred. Place in plastic bag and seal. Let steam for 15 minutes. Cool, remove skins, seeds, and stems. Dice.
To assemble, place tortilla on a flat surface. Add 2 oz. shrimp, 1 oz. spinach, ½oz. red bell pepper, and ½ oz. of queso blanco. Roll tightly and place in a hotel pan sprayed with pan release, seam side down. Repeat until there are enough enchiladas to fill 2 pans. Ladle the soup base mixture over enchiladas. Top with remaining queso blanco.
Bake at 350˚F for 30 minutes.