In a small bowl, whisk together the lemon juice, salt, and honey. Stream in the olive oil and whisk until well combined. Add the scallions and stir.
Place the veggies (zucchini, yellow squash, bell peppers, and red onion) in a large rimmed pan or baking dish. Pour over ¼ cup of the dressing, tossing to coat. Reserve the remaining dressing for the bowls.
Heat an outdoor grill or grill pan to medium heat. Grill the veggies for 5 minutes, flip, then grill an additional 4-5 minutes until golden and just cooked through. Remove to a pan and set aside.
Assemble by dividing the quinoa evenly between 4 bowls. Top each with the grilled veggies, arugula, cherry tomatoes, and hummus. Drizzle each with the remaining dressing, and serve.