Core the apple. Lay the apple on its side and cut crosswise into 1/4-inch-thick slices, about 9 slices.
Arrange the apples slices on a plate or work surface. Divide the nut butter evenly among the apple slices and spread it over their tops. Sprinkle the granola on top, dividing it evenly among the slices. Press the granola down slightly so it sticks to the nut butter.
Use homemade granola, or look for a low sugar variety.