In two bowls, toss the zucchini and onion with some olive oil and sprinkle with salt and pepper. Set aside.
Heat grill on high. Place a metal grill basket in the grill and get it hot.
Mix together the ricotta with lemon zest, salt, and pepper.
In a small bowl whisk together the dressing ingredients - olive oil, lemon juice, garlic, salt, and pepper.
Once the grill is hot, add the zucchini and cover the grill. Cook for 5 minutes.
Stir the squash and turn over the slices. Then mix in the onions. Cover the grill and cook for 10-15 minutes, or until both the squash and onion are cooked through and charred in spots.
Transfer the squash and onions to a serving plate. Dollop the ricotta around and pour over the dressing. Top with torn basil leaves. Serve.