Preheat the oven to 400 degrees.
Place all of the green beans, zucchini, lemon slices, and garlic on a large baking sheet. Drizzle the olive oil all over the veggies, and season with the onion powder, salt, and pepper. Use your hands to toss everything together to coat, and spread them out into an even layer.
Add the salmon fillets to the top of the veggies and drizzle them with a tiny bit more olive oil. Season each piece with a pinch of salt and pepper. Take a few of the lemon slices from the veggie mix and scatter them around and on top of the salmon.
Roast for 35-40 minutes, until the salmon is cooked through and the veggies are tender.
Divide onto plates and serve! You can serve this with rice if you want to add a starch to the meal.