The ornamental design for a mountablelighting apparatus, as shown and described.
FIG. 1 is a side perspective lighting surface view of a lighting apparatus showing the new design;
FIG. 2 is a lighting surface direct view thereof;
FIG. 3 is a lengthwise side view thereof;
FIG. 4 is a widthwise side view thereof; and,
FIG. 5 is a mounting direct view thereof.
The broken line showing of the lighting apparatus shows elements of a housing with side holes for mounting with screws to a portion of a vehicle, such as below running boards, with a plurality of LED's located in a central area that forms no part of the claimed design.