In a baking pan, arrange bread in a single layer. In a small bowl, whisk egg, milk and a pinch salt. Pour over bread; cover and refrigerate overnight. In the morning, lightly coat a skillet with cooking spray and heat over medium. Add bread and cook until browned on the bottom, about 4 minutes. Flip, top each piece with a slice of cheese and cook, covered, until cheese melts, about 3 minutes. Top with tomatoes and basil.