1.Grease a 19cm-deep square cake pan; line base and sides with baking paper.
2.In a large saucepan, bring water and stock to the boil; gradually stir in polenta. Reduce heat; simmer, stirring constantly, for about 10 minutes, or until polenta thickens.
3.Stir in zucchini, olives, cheese and tomato. Spread polenta mixture into pan; cover with plastic wrap, refrigerate for about 1 hour, or until polenta is firm.
4.Turn polenta onto board; cut in half. Cut each half into six slices.
5.In a large frying pan, heat oil on medium heat; cook polenta for about 2-3 minutes, or until browned both sides.