Adjust oven rack to lowest position, place rimmed baking sheet on rack, and heat oven to 500 degrees. Cut broccoli horizontally at juncture of crowns and stalks. Cut crowns into 4 wedges if 3 to 4 inches in diameter or 6 wedges if 4 to 5 inches in diameter. Trim tough outer peel from stalks, then cut into ½-inch-thick planks about 2 to 3 inches long.

Toss broccoli with 3 tablespoons oil. Working quickly, lay broccoli in single layer, flat sides down, on preheated sheet. Roast until stalks are well browned and tender and florets are lightly browned, 9 to 11 minutes. Transfer broccoli to cutting board, let cool slightly, then cut into 1½-inch pieces.

Process remaining 2 tablespoons oil, half of avocado, vinegar, garlic, salt, and pepper in food processor until smooth, scraping down sides of bowl as needed; transfer to large serving bowl. Add

broccoli, remaining avocado, tomatoes, and basil and toss to combine. Season with salt and pepper to taste. Serve.