Bring a large pot of water to a boil. Add the broccoli and cook until vibrant green in colour, about 2 minutes. Drain well, cool in ice water, and then drain well again.
Arrange the broccoli in a 9x13 inch casserole. Drizzle the broccoli with the stock and melted butter; sprinkle with the bell pepper, salt, and pepper. (At this point, the casserole could be covered, stored in the fridge, and baked later.) Sprinkle the broccoli with the lemon zest. Cover with the foil and bake at 350 degrees for 20 minutes, or until heated through.