Heat oven to 375°F. Spread the hazelnuts on a rimmed baking sheet and toast, tossing occasionally, until fragrant, 5 to 6 minutes; roughly chop.
Meanwhile, fill a large saucepan with 1 inch of water and fit with a steamer basket (or fill a large pot with ½ inch of water). Bring to a simmer. Place the broccoli in the steamer basket, cover, and steam until tender, 4 to 5 minutes. Transfer to a platter.
Meanwhile in a small saucepan, cook the oil and garlic over low heat until the garlic is just golden, 4 to 6 minutes. Transfer to a small bowl and stir in the hazelnuts, lemon juice, and ½ teaspoon each salt and pepper. Drizzle over the broccoli.