Preheat oven to 450°
Slice veggies: I find it easiest to cut into small, thin-ish squares. Once your onion is peeled and root tip removed, cut in half, and cut each half into quarters to get square-ish shaped pieces, then peel apart the layers. Cut the pepper and eggplant into similar sizes for even cooking.
Set aside about a third of your peppers and just one or two pieces of onion as these will go in the salad raw.
Coat veggies to be roasted lightly with olive oil, salt, pepper, and thyme (leaves stripped from stem and roughly chopped) if you like. All these veggies can be eaten raw, so the cook time is really up to you. I like mine to become just a bit tender, but still have a little bite to them. Don't cook the life out of them until they become mush! About 10 minutes in the oven does the trick. Hot and fast!
While roasting, you can very finely slice your raw onion and pepper. We don't want large chunks of onion because its sharpness can overwhelm the palate! This step is optional but does create more texture in the final dish.
When veggies are finished roasting, toss with raw veggies, and serve with a squeeze of fresh lemon juice overtop. I personally am not a big fan of extra oil on my salads, though if you like you can finish with a drizzle of Olive Oil as well.