Thanks to Debrah for the recipe! I made some changes, and here's how I did it.
I grilled asparagus, mushrooms, mini peppers, onions, and whole tomatoes. I blanched with chopped garlic some green beans, then shocked them with cold water and lightly dressed them with vinaigrette. The tuna was grilled until just pink in the middle.
I covered a large platter with lettuce, and arranged everything on top. I used much less oil than called for in the vinaigrette, but the vegetables absorbed the sharpness of the vinegar nicely. The classic recipe also calls for olives, potatoes and hard-boiled eggs, but I'll do that next time. I also made a little salad of chickpeas, tomato and basil, but ran out of room on the platter so served it on the side.
Served four happy eaters, including two teens.