1Preheat oven to 425°F. Arrange bell peppers, zucchini, and red onion on a large sheet pan. Drizzle with 1.5 tbsp olive oil, season with half the salt and half the oregano, and toss. Roast for 10 minutes.
2Meanwhile, bring vegetable broth to a boil in a skillet. Stir in couscous, remove from heat, cover, and let sit for 5 minutes. Fluff with a fork and stir in minced garlic, capers, and olives. Set aside.
3Remove sheet pan from oven. Push vegetables to the sides and nestle salmon portions skin-side down in the center. Brush salmon with remaining 1.5 tbsp olive oil. Season salmon with remaining salt, pepper, and oregano. Squeeze juice from one lemon over everything and scatter cherry tomatoes around the pan.
4Return to oven and bake for 12–14 minutes, until salmon is opaque and flakes easily.
5Divide couscous among bowls. Top with roasted vegetables and a salmon portion. Garnish with fresh dill and serve with lemon wedges.