In a medium skillet cook zucchini and green onions in hot oil over medium-high heat for 3 to 5 minutes or until just tender and liquid is evaporated. Cool slightly.
In a large bowl combine egg, bread crumbs, mustard, thyme, and cayenne pepper. Add crabmeat and the zucchini mixture; mix well. Using about 1/4 cup mixture per crab cake, shape into eight 1/2-inch-thick patties.
For a charcoal grill, grill crab cakes on the greased rack of an uncovered grill directly over medium coals for 8 to 10 minutes or until golden, turning once halfway through grilling. (For a gas grill, preheat grill. Reduce heat to medium. Place crab cakes on greased grill rack over heat. Cover and grill as directed.)
To serve, arrange tomato slices and crab cakes on plates. Serve with Tomato Sour Cream Sauce and, if desired, lemon wedges.
Tomato Sour Cream Sauce
In a small bowl stir together sour cream, chopped tomato, lemon juice, and seasoned salt. Cover and chill until serving time.