Heat the oven to 400°F and grease a small baking dish.
Heat 2 tablespoons of the olive oil in a medium skillet over medium heat. Add 12 ounces grapes (off the stems) and cook, shaking the pan every couple of minutes until grapes are beginning to soften, about 5-8 minutes. Just as grapes start to soften, stir in the 2 teaspoons rosemary, 1 teaspoon lemon zest, 1/4 teaspoon kosher salt, and 1/8 teaspoon pepper. Cook 1 minute more. Remove from heat.
Roughly cut the 10 ounce log of goat cheese into slices and place in the prepared baking pan. It's okay if it crumbles. Spoon grape mixture over the goat cheese. Bake in the preheated oven for 15 minutes or until the cheese is melted and puffy.
While cheese is baking, heat remaining 1 tablespoon of the olive oil in a small frying pan over low heat. Add sage leaves and fry until crisp, flipping once, about 1-2 minute. Remove to a paper towel-lined plate.
Remove cheese from the oven and garnish with the 1/4 cup toasted walnuts and sage. Drizzle 1 tablespoon honey over the top Serve while warm with crackers and/or bread slices.