Heat the oven to 450ºF.

• Cut the tomatoes crosswise into ½-inch-thick slices.
• Cut the squash in half lengthwise, then on the diagonal ½ inch thick.
• Trim the stem ends from the snap peas and pull off the strings.
• Thinly slice the chives and put in a heat-proof bowl.

On a lightly-oiled sheet pan, arrange the tomato slices in an even layer and season generously with salt and pepper. Roast, turning halfway through, until soft and lightly charred, 18 to 20 minutes. While the tomatoes roast, make the chive oil.

In a pan over medium-high heat, warm 1 to 2 tablespoons oil until hot but not smoking. Pour the hot oil into the bowl with the chives, stir in as much harissa as you like, and set aside.

• Season the steaks generously with salt and pepper.

In the same pan used to warm the oil, cook the steaks over medium-high heat until well browned, 3 to 4 minutes per side for medium-rare, depending on thickness. Transfer the steaks to a plate and let rest. While the steaks cook, prepare the dressing.

• Coarsely chop the walnuts.
• Juice the lemon.
• Pick and finely chop the basil leaves; discard the stems.

In a small bowl, combine the walnuts, lemon juice, and basil, and season with salt and pepper.

In the same pan used for the steak, if dry, add 1 to 2 teaspoons oil. Add the squash and cook over medium-high heat, stirring, until starting to soften, 2 to 3 minutes. Add the snap peas and 2 tablespoons water and cook until crisp-tender, 1 to 2 minutes.
Transfer the squash mixture to a mixing bowl, add the roasted tomatoes and the basil-walnut dressing, and toss to coat.

Transfer the vegetables to individual plates. Place the steaks alongside, drizzle with some of the chive oil, and serve with the remaining chive oil on the side.