Position a rack in the upper third of the oven and preheat to 425 degrees F. Toss the squash with 1 tablespoon olive oil on a baking sheet; season with 1/2 teaspoon salt and a few grinds of pepper. Roast until tender and golden around the edges, 15 to 20 minutes.
Meanwhile, season the salmon with 1/2 teaspoon each salt and pepper and sprinkle with 2 tablespoons herbs. Refrigerate until ready to roast. Toss the tomatoes in a bowl with the scallions, the remaining 2 tablespoons herbs and 1 tablespoon olive oil, and 1/2 teaspoon salt; set aside.
Remove the squash from the oven and push to one side of the baking sheet. Put the salmon on the other side, herb-side up. Return to the oven and roast until the salmon is cooked through and the squash is browned, about 7 minutes. Serve the salmon and squash with the tomato salad.