Slice the zucchinis and eggplant into 1/2-inch thick rounds and planks respectively—this uniform thickness ensures even cooking on the grill. Halve the tomatoes and brussels sprouts, keeping the mini bell peppers whole. Slice the lemons into thin rounds. Pat the vegetables dry with paper towels to remove excess moisture, which helps them develop better color and char on the grill. In a large bowl, toss all prepared vegetables with the 4 tablespoons of olive oil, minced garlic, dried oregano, 3/4 teaspoon salt, and 1/2 teaspoon black pepper until evenly coated.

Heat your grill to medium-high heat. Working in batches to avoid overcrowding, arrange the seasoned vegetables directly on the grill grates. Grill for about 4 minutes on the first side without moving them—this creates beautiful char marks and caramelization. Flip each piece and grill for another 4 to 5 minutes until tender and lightly charred. I like to arrange the vegetables by cooking time, grilling the harder ones like brussels sprouts and eggplant first, then adding the quicker-cooking zucchini and tomatoes so everything finishes at roughly the same time.

While the vegetables are grilling, prepare the finishing dressing. In a small jar or bowl, whisk together the 1/3 cup extra virgin olive oil, fresh lemon juice, sumac, and a pinch of salt and pepper. The sumac adds a bright, tangy flavor that complements the smoky grilled vegetables beautifully—if you don't have sumac, a bit more lemon zest works as a substitute.

Transfer the grilled vegetables to a serving platter, arranging them attractively. Drizzle the lemon-sumac dressing from Step 3 over all the vegetables while they're still warm, which allows them to absorb the flavors. Scatter the lemon slices from Step 1 over the top for garnish and brightness. Serve immediately while the vegetables still have some warmth.