In a sauce pan over medium-high heat, reduce the port and sugar to ½ cup (this will take ~30-35 minutes).
While the port is reducing, heat 1 Tbsp olive oil in a large non-stick pan over medium heat and add the onions.
Cook, stirring frequently, until the onions have nicely caramelized, about 30-35 minutes. (If necessary, reduce heat and add a couple tablespoons of water to keep them from burning.)
Heat grill to medium-high.
When the port reduction is cool enough to touch, crumble the ground beef into a bowl and season with salt and pepper.
Drizzle ¼ cup port reduction over top and lightly mix with your hands.
Form slider patties (you'll get 8-9 2-oz patties) and cook to desired doneness, 2-3 minutes on each side.
Serve the sliders on buns of your choice, topped with caramelized onions, a spoonful of remaining port reduction, and crumbled goat cheese.