Cook linguine noodles according to package instructions. Drain the noodles well.
Meanwhile salt and pepper shrimp on both sides. In large skillet heat 1 tablespoon olive oil over medium high heat. Add shrimp and cook for 1 minute. Flip and cook for another 30-60 seconds. Do not overcrowd the pan so you may need to cook in batches. When cooked the exterior should be pink with red tails and the flesh is slightly opaque. If using large shrimp there may be additional cooking time. Remove shrimp from skillet and place on plate.
In same skillet heat tablespoon of olive oil over medium heat. Add onion and cook until slightly tender approximately 2-3 minutes. Reduce heat to low and add garlic and spinach and cook for additional 60 seconds. Remove from skillet and place on plate.
In same large skillet over medium low heat melt butter; whisk in flour. Cook 3-4 minutes whisking continuously until a light golden brown. Slowly add half and half; whisking constantly. Reduce heat to low and slowly stir in Parmesan. Add roasted red peppers, cooked shrimp and cooked vegetables. Toss to coat. Season with red pepper flakes and salt & pepper to taste
Straight shrimp are undercooked, shrimp that have just curled into a C-shape are perfectly cooked and shrimp that have twisted into an O-shape are terribly, irreparably overcooked.