Preheat the oven to 350 degrees F (175 degrees C). Spray a large sheet pan with cooking spray.
Mix shrimp and lemon-pepper seasoning together in a bowl.
Toss onions and bell pepper strips with olive oil and fajita seasoning in a large bowl until thoroughly coated. Arrange shrimp on one side of the prepared pan and vegetables on the other.
Bake in the preheated oven until shrimp are bright pink on the outside and the meat is opaque, about 30 minutes.
Meanwhile, stack tortillas on a microwave-safe plate and cover with a wet paper towel. Heat in the microwave for 45 seconds. Serve with shrimp fajitas.