Make the Dressing: Whisk vinegar with agave nectar and lime juice in a bowl. Slowly whisk in oil; add salt and pepper to taste. Set aside.
Prepare Salad: Steam or boil beets until cooked through, about 30 minutes. Let cool; peel and cut into a medium dice.
While beets are cooking prepare the rest of the ingredients. Heat a grill or grill pan over medium-low heat. Rub zucchini, corn, scallions and salmon with oil; sprinkle with salt. Grill vegetables and fish until browned and cooked through [flip once], about 20 minutes.
Cut zucchini and scallions into a medium dice. Cut corn off the cob. Break salmon into large pieces.
Toss grilled vegetables with lettuce, tomatoes, cilantro and basil; place on a large platter and top with salmon. Drizzle with vinaigrette; serve with lime quarters.