Preheat a grill or grill pan at medium-high heat. In a bowl, combine the zucchini, radishes, and asparagus with 2 tablespoons of the olive oil. Season with 3/4 teaspoon salt and 1/4 teaspoon pepper.
Place the vegetables on the hot grill and cook, uncovered, for 3 minutes. Turn the vegetables and cook for 3 minutes more. Continue cooking, turning every 3 minutes, until the vegetables are tender throughout; if they’re browning too quickly, move them to the edge of the grill or grill pan. Set aside the vegetables on a cutting board.
Meanwhile, make the dressing: in a food processor or blender, combine 1 tablespoon of the olive oil and the avocado, lime juice, mayonnaise, vinegar, and cilantro. Process until the mixture is smooth and creamy. Season to taste with salt and pepper.
To serve the salad, place the chopped lettuce in a serving bowl, add the remaining olive oil and 1/4 teaspoon salt, and a few grinds of pepper. Chop the grilled vegetables into bite-size pieces (asparagus on the bias, zucchini into chunks, radishes diced) and add them to the bowl. Toss the salad, then divide it between 2 dinner plates. Sprinkle each with the sunflower seeds and serve with the dressing on the side.