Whisk balsamic vinegar, 3 Tbsp oil, 1 tsp kosher salt, and 1/2 tsp pepper in small bowl. Finely grate 2 garlic cloves and whisk into marinade. Place steak in a resealable plastic bag. Pour marinade over steak, toss to coat, then let rest at room temperature for at least 1 hour.
Meanwhile, toss tomatoes and 1 tsp kosher salt in a colander set over a large bowl; let rest for 1 hour.
Prepare grill for medium-high heat or heat grill pan over medium-high; lightly oil grate or pan. Remove steaks from marinade and pat dry. Grill steaks, turning occasionally, until lightly charred on all sides and thermometer reads 125 degrees, 8-10 minutes for medium-rare. Transfer to a cutting board and let rest 10 minutes before slicing against the grain.
Brush zucchini with oil; season with 1/4 tsp kosher salt and 1/8 tsp pepper. Grill, turning occasionally, until zucchini is charred and tender, about 10 minutes. Meanwhile, grill bread alongside zucchini, turning occasionally, until lightly charred and crisp, about 5 minutes. Transfer remaining garlic clove and rub all over bread. Cut bread into 1" cubes.
Shake colander to thoroughly drain tomatoes, reserving the liquid into the bowl. Add the Fat Boy Apple Cider Honey Mustard Sauce and remaining 1/4 cup oil and 1/2 tsp pepper with tomato liquid and whisk to combine. Add kale and zucchini and toss to coat. Add tomatoes, bread and basil and toss just to combine. Top with steak and sprinkle with sea salt.
