Whisk together the molasses, red wine vinegar, Dijon mustard, olive oil, chopped fresh rosemary, low-sodium soy sauce, and chopped garlic in a 2-cup measuring cup.

Pour the marinade into a 1-gallon ziptop bag.

Add the London broil to the bag, ensuring it's fully coated with the marinade.

Refrigerate the London broil in the marinade for at least 1 hour, or up to 4 hours.

Remove the steak from the refrigerator 30 minutes before grilling to allow it to come to room temperature.

Heat a cast-iron grill pan or outdoor grill to medium-high heat.

Remove the London broil from the marinade, letting the excess marinade drip off.

Season the steak generously with kosher salt and freshly ground black pepper.

Grill the steak on each side for 10 to 12 minutes, for a total cooking time of 20 to 24 minutes, or until desired doneness.

Remove the steak from the grill and let it rest for 10 minutes before slicing across the grain.

Prepare the salad by adding grape tomatoes, zucchini (sliced lengthwise), red bell pepper (quartered), yellow bell pepper (quartered), and red onion (sliced) to a large rimmed baking sheet.

Drizzle with olive oil, then season evenly with kosher salt and freshly ground black pepper.

Toss to coat all vegetables in the oil and seasonings.

Place the vegetables in a grill basket.

Grill over medium-high heat until tender and lightly charred, about 5 minutes per side, flipping once.

If using an indoor grill pan, grill in batches to avoid overcrowding.

Remove the charred vegetables to a cutting board and let them cool slightly until easy to handle.

Chop the grilled vegetables into bite-sized pieces.

Add the chopped vegetables, roughly chopped fresh basil, and arugula to a large bowl.

Drizzle with balsamic vinegar and a small amount of olive oil.

Season with salt and pepper to taste.

Toss the salad gently to combine all ingredients.

Serve the grilled summer salad alongside the sliced London broil.