We claim the ornamental design for a food preparation unit, as shown and described.
FIG. 1 is a perspective view of the claimed design;
FIG. 2 is a top view of the claimed design of FIG. 1;
FIG. 3 is a rear view of the claimed design of FIG. 1;
FIG. 4 is a front view of the claimed design of FIG. 1;
FIG. 5 is a left view of the claimed design of FIG. 1; and,
FIG. 6 is a right view of the claimed design of FIG. 1.
The ornamental design which is claimed is shown in solid lines in the figures. The dash-dash broken lines show portions of the article and form no part of the claimed design. The dash-dot broken lines behind brackets show break lines and the appearance of any portion of the article between the break lines form no part of the claimed design.