To make glaze, scoop out a few spoonfuls of raspberry jam into a bowl. Add just enough vinegar to thin it out. The ratio will completely depend on how thick your raspberry jam is. I’ve found some jams are much thinner than others. You can always add a little bit more jam if it gets to thin. After it is mixed together it should be thick enough to coat the back of a spoon and stay when you wipe a finger through it.
To assemble sandwich, spread glaze onto two slices of bread. Top with turkey, spinach, tomatoes, and cheese. Butter top of sandwich and place in a grill pan on medium heat. While the bottom is browning butter the opposite side of the bread. Flip and cook until browned on the second side.