Heat butter in a saucepan over medium heat. Cook and stir onion until slightly tender, about 5 minutes. Add Wahlburgers Beef, Worcestershire sauce, salt, black pepper and garlic powder, cook and stir until Wahlburgers Beef is browned and crumbly, about 10 minutes. Remove from heat, drain liquid from Wahlburgers Beef, and let sit for 2 minutes.
Heat a griddle or flat pan over medium heat and apply cooking spray.
Place 1 tortilla on the hot griddle, top some of the Colby cheese, 1/4 of the beef mixture, 1 teaspoon of ketchup, 1 teaspoon of mustard, 1 teaspoon of relish. Top with more Colby cheese and 1 tortilla. Flatten the quesadilla with a spatula and cook until browned and cheese is melted, about 3 to 5 minutes.
Cut the quesadilla into 4 pieces. Repeat the steps for remaining quesadillas.