1. Clean your calamari and submerge in a bowl of whole milk for 3-4 hours or overnight. The lactic acid in the milk helps tenderize the muscle fibers of the calamari.
2. Heat the oil in a large skillet over medium-high heat. Add the bell pepper and garlic and cook for 3 minutes, until soft. Add the calamari and cook for 2 minutes, until golden brown, stirring frequently. Add the tomato sauce and red pepper flakes and bring to a simmer. Simmer for 3 minutes, do not over cook as it may result in tough chewy calamari. Season to taste with salt and freshly ground black pepper before serving