For the apples and filling: Preheat the oven to 350 degrees F. Line a baking sheet with parchment.
Halve the apples across the equator. Scoop out the core of the apples, leaving a well in the center. Level the bottoms of the apples if needed.
In a large bowl, combine the peanut butter, yogurt, peanuts and agave. Fill the apple halves evenly and place them on the prepared baking sheet. Bake until the filling is set and the apples are slightly tender, 20 to 25 minutes.
For the topping: Add the jelly to a small bowl, then add a few drops of hot water at a time to loosen it, stirring, until you reach a syrup consistency.
Sprinkle the toast pieces over the top of the apples, drizzle the jelly syrup on top and sprinkle lightly with salt.