Preheat the oven to 450 degrees. In a small bowl, melt 3 tbsp. butter in the microwave, then stir in the garlic. Spread the broccoli in a single layer on a rimmed baking sheet; drizzle the the garlic butter. Roast until tender, about 10 minutes.
Meanwhile, in a large skillet, cook the bacon over medium-high heat until crisp, about 10 minutes; transfer to a paper-towel-lined plate. Reserve the skillet, discarding all but 1 tbsp. of the bacon fat.
In a large pot of boiling, salted water, cook the couscous until just al dente, 5 to 6 minutes; drain.
Add the corn and scallions to the reserved skillet and cook over medium-high heat until warmed through, about 2 minutes. Add the couscous and chicken stock and simmer until the liquid is absorbed, about 2 minutes; season with salt and pepper. Stir in the remaining 2 tbsp. butter, the cheese and reserved bacon. Serve with the broccoli.