Heat a large skillet over MEDIUM-HIGH heat on stove top. Add 1 Tbsp. oil to skillet and heat.
Add diced bell peppers and onions to the pan. Stir and sauté for 10 minutes or until onions start to brown. Add shredded carrots to the skillet, stir, and cook for an additional 5-7 minutes until carrots start to soften. Transfer veggies to a bowl and keep warm.
Add Ground Beef to the hot skillet. Break the beef into crumbles with a spatula and cook the meat until it is fully browned, about 8-10 minutes. Carefully drain off any excess fat, then add the taco seasoning and the veggies to the skillet with the beef.
Heat another medium-sized skillet over MEDIUM-HIGH heat on stove top. While the skillet is heating, assemble each quesadilla: place one tortilla in the pan and layer with 2 Tbsp. of cheese, ½ cup of the beef and veggie mixture and an additional 2 Tbsp. of cheese, carefully spreading each layer out evenly on the tortilla. Top with a second tortilla. Repeat this process three times to make a total of 4 quesadillas.
Place the quesadillas in the pan and cook on the first side for 5-7 minutes until they start to brown. Flip the quesadillas and cook for an additional 4-5 minutes or until crispy.