The ornamental design for a spoon with a slanted handle, as shown and described.
FIG. 1 shows a top view of a spoon with a slanted handle;
FIG. 2 shows a front view thereof;
FIG. 3 shows a rear view thereof;
FIG. 4 shows a second top view thereof;
FIG. 5 shows a bottom view thereof;
FIG. 6 shows a left side view thereof;
FIG. 7 shows a right side view thereof; and,
FIG. 8 shows a perspective view thereof.
The dashed lines are for the purpose of illustrating portions of the spoon with a slanted handle and form no part of the claimed design. The dotted lines on the surface portions indicate contour and not surface decoration.