Wash lettuce and tomatoes. Tear lettuce and cut tomatoes into bite-sized pieces, and transfer to a platter. Roughly chop basil and add to salad.
Slice eggplant and zucchini into bite-sized pieces. Heat pan over medium-high heat and coat generously with olive oil. When oil is hot, add eggplant and zucchini and fry, stirring often, until well browned. Season with salt and pepper to taste. Set aside until cooled slightly, then add to salad.
Roughly chop garlic and tarragon. Add to a bowl with egg, mustard, vinegar, and honey, and blend with an immersion blender until foamy. Stream in olive oil until smooth and thickened. Season with salt and pepper to taste.
Heat the same pan used to fry the vegetables over medium-high heat. Add a bit more oil if needed, and once hot, add the steak. Sear briefly on each side until well browned. Add butter to pan along with herbs and baste steak until cooked to desired doneness (medium-rare recommended).
Let steak rest until cool enough to handle. Slice against the grain, then transfer to the salad. Serve salad with aioli for dipping or drizzling. Enjoy!