Preheat your grill to medium-high heat (400ºF).
On four large pieces of aluminum foil, evenly distribute the sliced vegetables, placing them in the center.
Place a salmon fillet on top of each vegetable bed. Drizzle with olive oil, then sprinkle garlic powder, salt, and pepper over each fillet.
Fold the edges of the foil over, sealing the salmon and vegetables inside to create a pack.
Grill the foil packs for about 15 minutes, until the salmon is cooked through and vegetables are tender.
Open the packs carefully to avoid steam, garnish with lemon slices, and serve immediately.