Adjust rack to top position and preheat oven to 425 degrees. In a medium pot (large pot for 4 servings), bring 5 cups water (8 cups for 4) to a boil, then reduce to a low simmer. Wash and dry produce.
Cut broccoli into bite-size pieces if necessary. Trim and thinly slice scallions, separating whites from greens.
Toss broccoli on a baking sheet with a drizzle of oil, salt, and pepper. Roast until browned and tender, 15-20 minutes.
Pat chicken* or salmon* dry with paper towels; season with salt and pepper. Heat a drizzle of oil in a large, preferably nonstick, pan over medium-high heat. Add chicken or salmon (skin sides down); cook chicken until cooked through, 3-5 minutes per side, or cook salmon until skin is crisp, 5-7 minutes, then flip and cook until cooked through, 1-2 minutes more. Turn off heat; transfer to a cutting board to rest. Wipe out pan.