Preheat the oven to 400°F. Toss the broccoli with 1 tablespoon olive oil, salt, and pepper. Spread in a single layer on a sheet pan. Roast 15 to 20 minutes, until tender with browned edges. Remove from the oven and set aside.
While the broccoli cooks, pat the salmon dry with a paper towel and season both sides with salt and pepper.
Heat a cast iron or stainless skillet over medium-high heat. Add the remaining olive oil. Place the salmon in the pan. If using skin-on salmon, place it skin-side down.
Cook 3 to 4 minutes, or until the fish releases easily from the pan.
Flip carefully and cook another 2 to 3 minutes, depending on thickness. Reduce heat to low.
Add the butter and smashed garlic to the pan. Let the garlic cook gently in the butter for about 1 minute, until softened but not browned.
Tilt the pan and spoon the butter and garlic over the salmon for about 30 seconds.
Squeeze fresh lemon juice over the top and spoon some of the softened garlic onto each fillet when serving.