Preheat your grill to medium-high heat (around 400°F).
Brush the zucchini, peppers, and onion slices with olive oil and season with salt and pepper.
Place the vegetables on the grill, adding the cherry tomatoes in a grill basket or on a piece of foil. Grill for 4-5 minutes per side, or until you see nice grill marks and the vegetables are tender but not mushy.
While the vegetables are grilling, prepare the dressing by whisking together lemon juice, olive oil, minced garlic, honey, and Dijon mustard in a small bowl. Season with salt and pepper to taste.
Once grilled, let the vegetables cool for about 5 minutes, then cut them into bite-sized pieces.
In a large serving bowl, arrange the mixed greens, top with the grilled vegetables, and sprinkle with torn basil leaves and crumbled feta if using.
Drizzle with the lemon dressing just before serving.