Preheat a grill pan over medium-high heat or preheat a gas or charcoal grill. Drizzle the romaine lettuce, corn, zucchini and shrimp with olive oil. Season with salt and pepper. Grill the romaine lettuce, turning occasionally, until crisp-tender and browned in spots, about 2 minutes. Grill the corn and zucchini for 2 minutes on all sides until crisp-tender.
Grill the shrimp for about 2-3 minutes on each side until the meat is opaque and cooked through.
Coarsely chop the grilled lettuce and place in a large salad bowl. Using a sharp knife, remove the kernels from the corn and add to the salad bowl. Chop the zucchini into 1/2-inch pieces and add to the bowl. Cut the shrimp into 1/2-inch pieces and add to the bowl. Add the butter lettuce, tomatoes and avocado to the bowl.
In a small bowl, whisk together the lemon juice, olive oil and agave nectar until smooth. Season with salt and pepper, to taste.
Pour the dressing over the salad and toss until all the ingredients are coated. Garnish the salad with tortilla strips and serve.