Preheat grill. Using a sharp knife, make 3-4 slits into the flesh of each perch on both sides. Oil and season. Stuff 5 sprigs of sage into the cavity of each perch. Place the perch on the grill and cook for 4 minutes, flip and place the tomatoes and zucchini on the grill. Cook for 4 minutes, flipping the tomatoes and zucchini as needed. Transfer to serving plates and drizzle with olive oil.