Heat a large skillet over medium-high heat and add 2 tablespoons of neutral oil, coating the surface.
Add diced onion and chopped bell pepper; cook, stirring occasionally, for 5 to 6 minutes until onions are translucent and peppers soften.
Reduce heat to medium and stir in taco seasoning to coat vegetables.
Add shrimp and cook for 3 to 5 minutes, stirring occasionally, until shrimp turn opaque and curl slightly.
Remove skillet from heat, sprinkle lime juice over the shrimp and vegetables, stir, and set aside.
Heat another skillet over medium heat and add ½ tablespoon butter, swirling to coat.
Place one flour tortilla flat in the skillet; spoon about ⅓ cup shrimp mixture on half of the tortilla and top with ½ cup shredded cheese.
Cook for about 90 seconds until the bottom is lightly browned.
Fold the tortilla over the filling, press gently with a spatula, flip, and cook for 1 to 2 minutes until the second side is browned.
Sprinkle with salt to taste and transfer to a plate.
Repeat with remaining tortillas, shrimp, and cheese until all quesadillas are cooked.
Serve warm with optional toppings and sides.