Marinate the steak
Combine the oil, garlic, rosemary, thyme, ½ tsp. salt, and ½ tsp. pepper in a zip-top bag large enough to hold the steak.
Add the steak and marinate for at least 1 hour at room temperature, or up to 6 hours in the refrigerator
Grill the Steak and Veggies
Prepare a medium-high (400°F to 475°F) gas or charcoal grill fire.
Meanwhile, in a small bowl, combine 2 Tbs. of the basil and 1 Tbs. of the oil with the vinegar, parsley, and garlic. Season with salt and pepper and set aside.
Brush the peppers, squash, zucchini, and corn with 1 Tbs. oil and season generously with salt and pepper.
Grill, turning occasionally, until tender with nice grill marks, 10 to 15 minutes.
Arrange all but the corn on a large platter and drizzle with the vinaigrette.
Remove the steak from the marinade, cut into manageable pieces for grilling, if you like, season generously with salt and pepper, and grill, flipping once until grill marks form on both sides and cooked to your liking, about 3 minutes per side for medium-rare (135°F).
Transfer to a cutting board and let rest for 5 minutes.
Cut the corn from the cob and transfer to a medium bowl. Add the tomatoes and the remaining 1 Tbs. oil and 1 Tbs. basil. Season with salt and toss gently.
Spoon half of the corn and tomato mixture over the other vegetables.
Slice the steak with the grain into 4- to 5-inch pieces, then slice thinly against the grain and arrange over the vegetables.
Scatter the remaining corn and tomatoes over the steak. Sprinkle with the scallions and sea salt, if using, and serve.