Carefully cut the top off the cob loaf, set aside and hollow out the middle to leave a shell, without making walls too thin.
Spread the pesto over the bottom and part way up the walls of the cobb. Cover the base with ²⁄³ spinach leaves, then layer with beef slices, roasted capsicum, eggplant, semi-dried tomatoes, basil leaves and the remaining spinach. Spread the inside of the cobb top with tomato relish, and place this top back on filled cob.
Wrap in cling film or foil until ready to serve. When ready to eat, cut cobb into four wedges.