Brush the baguette slices with 1 tbsp. of oil and a sprinkle of fleur de sel. Toast on baking sheets until golden brown, about 5 minutes. Set aside.
Add the additional tsp. of oil to a large nonstick skillet over medium-low heat. Add in the onion and cook over medium-low heat until caramelized, and golden, about 25-30 minutes.
Add in the cherries, honey, balsamic and red wine. Increase the heat and cook until the cherries easily smash with a spoon and the mixture looks jammy. Set aside.
To serve, lay down a few thin slices of plum onto each piece of toast. Top with a layer of the cherry onion jam, a sprinkle of pistachios and a few shavings of parmigiano reggiano. Enjoy at room temperature.